[IA64] move XP and XPC to drivers/misc/sgi-xp

Move XPC and XPNET from arch/ia64/sn/kernel to drivers/misc/sgi-xp.

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 2379 insertions, 0 deletions

diff --git a/drivers/misc/sgi-xp/xpc_channel.c b/drivers/misc/sgi-xp/xpc_channel.c
new file mode 100644
index 000000000000..d7a215eeaaf6
--- /dev/null
+++ b/drivers/misc/sgi-xp/xpc_channel.c
@@ -0,0 +1,2379 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (c) 2004-2008 Silicon Graphics, Inc.  All Rights Reserved.
+ */
+
+
+/*
+ * Cross Partition Communication (XPC) channel support.
+ *
+ *      This is the part of XPC that manages the channels and
+ *      sends/receives messages across them to/from other partitions.
+ *
+ */
+
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/cache.h>
+#include <linux/interrupt.h>
+#include <linux/mutex.h>
+#include <linux/completion.h>
+#include <asm/sn/bte.h>
+#include <asm/sn/sn_sal.h>
+#include "xpc.h"
+
+
+/*
+ * Guarantee that the kzalloc'd memory is cacheline aligned.
+ */
+static void *
+xpc_kzalloc_cacheline_aligned(size_t size, gfp_t flags, void **base)
+{
+        /* see if kzalloc will give us cachline aligned memory by default */
+        *base = kzalloc(size, flags);
+        if (*base == NULL) {
+                return NULL;
+        }
+        if ((u64) *base == L1_CACHE_ALIGN((u64) *base)) {
+                return *base;
+        }
+        kfree(*base);
+
+        /* nope, we'll have to do it ourselves */
+        *base = kzalloc(size + L1_CACHE_BYTES, flags);
+        if (*base == NULL) {
+                return NULL;
+        }
+        return (void *) L1_CACHE_ALIGN((u64) *base);
+}
+
+
+/*
+ * Set up the initial values for the XPartition Communication channels.
+ */
+static void
+xpc_initialize_channels(struct xpc_partition *part, partid_t partid)
+{
+        int ch_number;
+        struct xpc_channel *ch;
+
+
+        for (ch_number = 0; ch_number < part->nchannels; ch_number++) {
+                ch = &part->channels[ch_number];
+
+                ch->partid = partid;
+                ch->number = ch_number;
+                ch->flags = XPC_C_DISCONNECTED;
+
+                ch->local_GP = &part->local_GPs[ch_number];
+                ch->local_openclose_args =
+                                        &part->local_openclose_args[ch_number];
+
+                atomic_set(&ch->kthreads_assigned, 0);
+                atomic_set(&ch->kthreads_idle, 0);
+                atomic_set(&ch->kthreads_active, 0);
+
+                atomic_set(&ch->references, 0);
+                atomic_set(&ch->n_to_notify, 0);
+
+                spin_lock_init(&ch->lock);
+                mutex_init(&ch->msg_to_pull_mutex);
+                init_completion(&ch->wdisconnect_wait);
+
+                atomic_set(&ch->n_on_msg_allocate_wq, 0);
+                init_waitqueue_head(&ch->msg_allocate_wq);
+                init_waitqueue_head(&ch->idle_wq);
+        }
+}
+
+
+/*
+ * Setup the infrastructure necessary to support XPartition Communication
+ * between the specified remote partition and the local one.
+ */
+enum xpc_retval
+xpc_setup_infrastructure(struct xpc_partition *part)
+{
+        int ret, cpuid;
+        struct timer_list *timer;
+        partid_t partid = XPC_PARTID(part);
+
+
+        /*
+         * Zero out MOST of the entry for this partition. Only the fields
+         * starting with `nchannels' will be zeroed. The preceding fields must
+         * remain `viable' across partition ups and downs, since they may be
+         * referenced during this memset() operation.
+         */
+        memset(&part->nchannels, 0, sizeof(struct xpc_partition) -
+                                offsetof(struct xpc_partition, nchannels));
+
+        /*
+         * Allocate all of the channel structures as a contiguous chunk of
+         * memory.
+         */
+        part->channels = kzalloc(sizeof(struct xpc_channel) * XPC_NCHANNELS,
+                                                                GFP_KERNEL);
+        if (part->channels == NULL) {
+                dev_err(xpc_chan, "can't get memory for channels\n");
+                return xpcNoMemory;
+        }
+
+        part->nchannels = XPC_NCHANNELS;
+
+
+        /* allocate all the required GET/PUT values */
+
+        part->local_GPs = xpc_kzalloc_cacheline_aligned(XPC_GP_SIZE,
+                                        GFP_KERNEL, &part->local_GPs_base);
+        if (part->local_GPs == NULL) {
+                kfree(part->channels);
+                part->channels = NULL;
+                dev_err(xpc_chan, "can't get memory for local get/put "
+                        "values\n");
+                return xpcNoMemory;
+        }
+
+        part->remote_GPs = xpc_kzalloc_cacheline_aligned(XPC_GP_SIZE,
+                                        GFP_KERNEL, &part->remote_GPs_base);
+        if (part->remote_GPs == NULL) {
+                dev_err(xpc_chan, "can't get memory for remote get/put "
+                        "values\n");
+                kfree(part->local_GPs_base);
+                part->local_GPs = NULL;
+                kfree(part->channels);
+                part->channels = NULL;
+                return xpcNoMemory;
+        }
+
+
+        /* allocate all the required open and close args */
+
+        part->local_openclose_args = xpc_kzalloc_cacheline_aligned(
+                                        XPC_OPENCLOSE_ARGS_SIZE, GFP_KERNEL,
+                                        &part->local_openclose_args_base);
+        if (part->local_openclose_args == NULL) {
+                dev_err(xpc_chan, "can't get memory for local connect args\n");
+                kfree(part->remote_GPs_base);
+                part->remote_GPs = NULL;
+                kfree(part->local_GPs_base);
+                part->local_GPs = NULL;
+                kfree(part->channels);
+                part->channels = NULL;
+                return xpcNoMemory;
+        }
+
+        part->remote_openclose_args = xpc_kzalloc_cacheline_aligned(
+                                        XPC_OPENCLOSE_ARGS_SIZE, GFP_KERNEL,
+                                        &part->remote_openclose_args_base);
+        if (part->remote_openclose_args == NULL) {
+                dev_err(xpc_chan, "can't get memory for remote connect args\n");
+                kfree(part->local_openclose_args_base);
+                part->local_openclose_args = NULL;
+                kfree(part->remote_GPs_base);
+                part->remote_GPs = NULL;
+                kfree(part->local_GPs_base);
+                part->local_GPs = NULL;
+                kfree(part->channels);
+                part->channels = NULL;
+                return xpcNoMemory;
+        }
+
+
+        xpc_initialize_channels(part, partid);
+
+        atomic_set(&part->nchannels_active, 0);
+        atomic_set(&part->nchannels_engaged, 0);
+
+
+        /* local_IPI_amo were set to 0 by an earlier memset() */
+
+        /* Initialize this partitions AMO_t structure */
+        part->local_IPI_amo_va = xpc_IPI_init(partid);
+
+        spin_lock_init(&part->IPI_lock);
+
+        atomic_set(&part->channel_mgr_requests, 1);
+        init_waitqueue_head(&part->channel_mgr_wq);
+
+        sprintf(part->IPI_owner, "xpc%02d", partid);
+        ret = request_irq(SGI_XPC_NOTIFY, xpc_notify_IRQ_handler, IRQF_SHARED,
+                                part->IPI_owner, (void *) (u64) partid);
+        if (ret != 0) {
+                dev_err(xpc_chan, "can't register NOTIFY IRQ handler, "
+                        "errno=%d\n", -ret);
+                kfree(part->remote_openclose_args_base);
+                part->remote_openclose_args = NULL;
+                kfree(part->local_openclose_args_base);
+                part->local_openclose_args = NULL;
+                kfree(part->remote_GPs_base);
+                part->remote_GPs = NULL;
+                kfree(part->local_GPs_base);
+                part->local_GPs = NULL;
+                kfree(part->channels);
+                part->channels = NULL;
+                return xpcLackOfResources;
+        }
+
+        /* Setup a timer to check for dropped IPIs */
+        timer = &part->dropped_IPI_timer;
+        init_timer(timer);
+        timer->function = (void (*)(unsigned long)) xpc_dropped_IPI_check;
+        timer->data = (unsigned long) part;
+        timer->expires = jiffies + XPC_P_DROPPED_IPI_WAIT;
+        add_timer(timer);
+
+        /*
+         * With the setting of the partition setup_state to XPC_P_SETUP, we're
+         * declaring that this partition is ready to go.
+         */
+        part->setup_state = XPC_P_SETUP;
+
+
+        /*
+         * Setup the per partition specific variables required by the
+         * remote partition to establish channel connections with us.
+         *
+         * The setting of the magic # indicates that these per partition
+         * specific variables are ready to be used.
+         */
+        xpc_vars_part[partid].GPs_pa = __pa(part->local_GPs);
+        xpc_vars_part[partid].openclose_args_pa =
+                                        __pa(part->local_openclose_args);
+        xpc_vars_part[partid].IPI_amo_pa = __pa(part->local_IPI_amo_va);
+        cpuid = raw_smp_processor_id(); /* any CPU in this partition will do */
+        xpc_vars_part[partid].IPI_nasid = cpuid_to_nasid(cpuid);
+        xpc_vars_part[partid].IPI_phys_cpuid = cpu_physical_id(cpuid);
+        xpc_vars_part[partid].nchannels = part->nchannels;
+        xpc_vars_part[partid].magic = XPC_VP_MAGIC1;
+
+        return xpcSuccess;
+}
+
+
+/*
+ * Create a wrapper that hides the underlying mechanism for pulling a cacheline
+ * (or multiple cachelines) from a remote partition.
+ *
+ * src must be a cacheline aligned physical address on the remote partition.
+ * dst must be a cacheline aligned virtual address on this partition.
+ * cnt must be an cacheline sized
+ */
+static enum xpc_retval
+xpc_pull_remote_cachelines(struct xpc_partition *part, void *dst,
+                                const void *src, size_t cnt)
+{
+        bte_result_t bte_ret;
+
+
+        DBUG_ON((u64) src != L1_CACHE_ALIGN((u64) src));
+        DBUG_ON((u64) dst != L1_CACHE_ALIGN((u64) dst));
+        DBUG_ON(cnt != L1_CACHE_ALIGN(cnt));
+
+        if (part->act_state == XPC_P_DEACTIVATING) {
+                return part->reason;
+        }
+
+        bte_ret = xp_bte_copy((u64) src, (u64) dst, (u64) cnt,
+                                        (BTE_NORMAL | BTE_WACQUIRE), NULL);
+        if (bte_ret == BTE_SUCCESS) {
+                return xpcSuccess;
+        }
+
+        dev_dbg(xpc_chan, "xp_bte_copy() from partition %d failed, ret=%d\n",
+                XPC_PARTID(part), bte_ret);
+
+        return xpc_map_bte_errors(bte_ret);
+}
+
+
+/*
+ * Pull the remote per partition specific variables from the specified
+ * partition.
+ */
+enum xpc_retval
+xpc_pull_remote_vars_part(struct xpc_partition *part)
+{
+        u8 buffer[L1_CACHE_BYTES * 2];
+        struct xpc_vars_part *pulled_entry_cacheline =
+                        (struct xpc_vars_part *) L1_CACHE_ALIGN((u64) buffer);
+        struct xpc_vars_part *pulled_entry;
+        u64 remote_entry_cacheline_pa, remote_entry_pa;
+        partid_t partid = XPC_PARTID(part);
+        enum xpc_retval ret;
+
+
+        /* pull the cacheline that contains the variables we're interested in */
+
+        DBUG_ON(part->remote_vars_part_pa !=
+                                L1_CACHE_ALIGN(part->remote_vars_part_pa));
+        DBUG_ON(sizeof(struct xpc_vars_part) != L1_CACHE_BYTES / 2);
+
+        remote_entry_pa = part->remote_vars_part_pa +
+                        sn_partition_id * sizeof(struct xpc_vars_part);
+
+        remote_entry_cacheline_pa = (remote_entry_pa & ~(L1_CACHE_BYTES - 1));
+
+        pulled_entry = (struct xpc_vars_part *) ((u64) pulled_entry_cacheline +
+                                (remote_entry_pa & (L1_CACHE_BYTES - 1)));
+
+        ret = xpc_pull_remote_cachelines(part, pulled_entry_cacheline,
+                                        (void *) remote_entry_cacheline_pa,
+                                        L1_CACHE_BYTES);
+        if (ret != xpcSuccess) {
+                dev_dbg(xpc_chan, "failed to pull XPC vars_part from "
+                        "partition %d, ret=%d\n", partid, ret);
+                return ret;
+        }
+
+
+        /* see if they've been set up yet */
+
+        if (pulled_entry->magic != XPC_VP_MAGIC1 &&
+                                pulled_entry->magic != XPC_VP_MAGIC2) {
+
+                if (pulled_entry->magic != 0) {
+                        dev_dbg(xpc_chan, "partition %d's XPC vars_part for "
+                                "partition %d has bad magic value (=0x%lx)\n",
+                                partid, sn_partition_id, pulled_entry->magic);
+                        return xpcBadMagic;
+                }
+
+                /* they've not been initialized yet */
+                return xpcRetry;
+        }
+
+        if (xpc_vars_part[partid].magic == XPC_VP_MAGIC1) {
+
+                /* validate the variables */
+
+                if (pulled_entry->GPs_pa == 0 ||
+                                pulled_entry->openclose_args_pa == 0 ||
+                                        pulled_entry->IPI_amo_pa == 0) {
+
+                        dev_err(xpc_chan, "partition %d's XPC vars_part for "
+                                "partition %d are not valid\n", partid,
+                                sn_partition_id);
+                        return xpcInvalidAddress;
+                }
+
+                /* the variables we imported look to be valid */
+
+                part->remote_GPs_pa = pulled_entry->GPs_pa;
+                part->remote_openclose_args_pa =
+                                        pulled_entry->openclose_args_pa;
+                part->remote_IPI_amo_va =
+                                      (AMO_t *) __va(pulled_entry->IPI_amo_pa);
+                part->remote_IPI_nasid = pulled_entry->IPI_nasid;
+                part->remote_IPI_phys_cpuid = pulled_entry->IPI_phys_cpuid;
+
+                if (part->nchannels > pulled_entry->nchannels) {
+                        part->nchannels = pulled_entry->nchannels;
+                }
+
+                /* let the other side know that we've pulled their variables */
+
+                xpc_vars_part[partid].magic = XPC_VP_MAGIC2;
+        }
+
+        if (pulled_entry->magic == XPC_VP_MAGIC1) {
+                return xpcRetry;
+        }
+
+        return xpcSuccess;
+}
+
+
+/*
+ * Get the IPI flags and pull the openclose args and/or remote GPs as needed.
+ */
+static u64
+xpc_get_IPI_flags(struct xpc_partition *part)
+{
+        unsigned long irq_flags;
+        u64 IPI_amo;
+        enum xpc_retval ret;
+
+
+        /*
+         * See if there are any IPI flags to be handled.
+         */
+
+        spin_lock_irqsave(&part->IPI_lock, irq_flags);
+        if ((IPI_amo = part->local_IPI_amo) != 0) {
+                part->local_IPI_amo = 0;
+        }
+        spin_unlock_irqrestore(&part->IPI_lock, irq_flags);
+
+
+        if (XPC_ANY_OPENCLOSE_IPI_FLAGS_SET(IPI_amo)) {
+                ret = xpc_pull_remote_cachelines(part,
+                                        part->remote_openclose_args,
+                                        (void *) part->remote_openclose_args_pa,
+                                        XPC_OPENCLOSE_ARGS_SIZE);
+                if (ret != xpcSuccess) {
+                        XPC_DEACTIVATE_PARTITION(part, ret);
+
+                        dev_dbg(xpc_chan, "failed to pull openclose args from "
+                                "partition %d, ret=%d\n", XPC_PARTID(part),
+                                ret);
+
+                        /* don't bother processing IPIs anymore */
+                        IPI_amo = 0;
+                }
+        }
+
+        if (XPC_ANY_MSG_IPI_FLAGS_SET(IPI_amo)) {
+                ret = xpc_pull_remote_cachelines(part, part->remote_GPs,
+                                                (void *) part->remote_GPs_pa,
+                                                XPC_GP_SIZE);
+                if (ret != xpcSuccess) {
+                        XPC_DEACTIVATE_PARTITION(part, ret);
+
+                        dev_dbg(xpc_chan, "failed to pull GPs from partition "
+                                "%d, ret=%d\n", XPC_PARTID(part), ret);
+
+                        /* don't bother processing IPIs anymore */
+                        IPI_amo = 0;
+                }
+        }
+
+        return IPI_amo;
+}
+
+
+/*
+ * Allocate the local message queue and the notify queue.
+ */
+static enum xpc_retval
+xpc_allocate_local_msgqueue(struct xpc_channel *ch)
+{
+        unsigned long irq_flags;
+        int nentries;
+        size_t nbytes;
+
+
+        // >>> may want to check for ch->flags & XPC_C_DISCONNECTING between
+        // >>> iterations of the for-loop, bail if set?
+
+        // >>> should we impose a minimum #of entries? like 4 or 8?
+        for (nentries = ch->local_nentries; nentries > 0; nentries--) {
+
+                nbytes = nentries * ch->msg_size;
+                ch->local_msgqueue = xpc_kzalloc_cacheline_aligned(nbytes,
+                                                GFP_KERNEL,
+                                                &ch->local_msgqueue_base);
+                if (ch->local_msgqueue == NULL) {
+                        continue;
+                }
+
+                nbytes = nentries * sizeof(struct xpc_notify);
+                ch->notify_queue = kzalloc(nbytes, GFP_KERNEL);
+                if (ch->notify_queue == NULL) {
+                        kfree(ch->local_msgqueue_base);
+                        ch->local_msgqueue = NULL;
+                        continue;
+                }
+
+                spin_lock_irqsave(&ch->lock, irq_flags);
+                if (nentries < ch->local_nentries) {
+                        dev_dbg(xpc_chan, "nentries=%d local_nentries=%d, "
+                                "partid=%d, channel=%d\n", nentries,
+                                ch->local_nentries, ch->partid, ch->number);
+
+                        ch->local_nentries = nentries;
+                }
+                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                return xpcSuccess;
+        }
+
+        dev_dbg(xpc_chan, "can't get memory for local message queue and notify "
+                "queue, partid=%d, channel=%d\n", ch->partid, ch->number);
+        return xpcNoMemory;
+}
+
+
+/*
+ * Allocate the cached remote message queue.
+ */
+static enum xpc_retval
+xpc_allocate_remote_msgqueue(struct xpc_channel *ch)
+{
+        unsigned long irq_flags;
+        int nentries;
+        size_t nbytes;
+
+
+        DBUG_ON(ch->remote_nentries <= 0);
+
+        // >>> may want to check for ch->flags & XPC_C_DISCONNECTING between
+        // >>> iterations of the for-loop, bail if set?
+
+        // >>> should we impose a minimum #of entries? like 4 or 8?
+        for (nentries = ch->remote_nentries; nentries > 0; nentries--) {
+
+                nbytes = nentries * ch->msg_size;
+                ch->remote_msgqueue = xpc_kzalloc_cacheline_aligned(nbytes,
+                                                GFP_KERNEL,
+                                                &ch->remote_msgqueue_base);
+                if (ch->remote_msgqueue == NULL) {
+                        continue;
+                }
+
+                spin_lock_irqsave(&ch->lock, irq_flags);
+                if (nentries < ch->remote_nentries) {
+                        dev_dbg(xpc_chan, "nentries=%d remote_nentries=%d, "
+                                "partid=%d, channel=%d\n", nentries,
+                                ch->remote_nentries, ch->partid, ch->number);
+
+                        ch->remote_nentries = nentries;
+                }
+                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                return xpcSuccess;
+        }
+
+        dev_dbg(xpc_chan, "can't get memory for cached remote message queue, "
+                "partid=%d, channel=%d\n", ch->partid, ch->number);
+        return xpcNoMemory;
+}
+
+
+/*
+ * Allocate message queues and other stuff associated with a channel.
+ *
+ * Note: Assumes all of the channel sizes are filled in.
+ */
+static enum xpc_retval
+xpc_allocate_msgqueues(struct xpc_channel *ch)
+{
+        unsigned long irq_flags;
+        enum xpc_retval ret;
+
+
+        DBUG_ON(ch->flags & XPC_C_SETUP);
+
+        if ((ret = xpc_allocate_local_msgqueue(ch)) != xpcSuccess) {
+                return ret;
+        }
+
+        if ((ret = xpc_allocate_remote_msgqueue(ch)) != xpcSuccess) {
+                kfree(ch->local_msgqueue_base);
+                ch->local_msgqueue = NULL;
+                kfree(ch->notify_queue);
+                ch->notify_queue = NULL;
+                return ret;
+        }
+
+        spin_lock_irqsave(&ch->lock, irq_flags);
+        ch->flags |= XPC_C_SETUP;
+        spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+        return xpcSuccess;
+}
+
+
+/*
+ * Process a connect message from a remote partition.
+ *
+ * Note: xpc_process_connect() is expecting to be called with the
+ * spin_lock_irqsave held and will leave it locked upon return.
+ */
+static void
+xpc_process_connect(struct xpc_channel *ch, unsigned long *irq_flags)
+{
+        enum xpc_retval ret;
+
+
+        DBUG_ON(!spin_is_locked(&ch->lock));
+
+        if (!(ch->flags & XPC_C_OPENREQUEST) ||
+                                !(ch->flags & XPC_C_ROPENREQUEST)) {
+                /* nothing more to do for now */
+                return;
+        }
+        DBUG_ON(!(ch->flags & XPC_C_CONNECTING));
+
+        if (!(ch->flags & XPC_C_SETUP)) {
+                spin_unlock_irqrestore(&ch->lock, *irq_flags);
+                ret = xpc_allocate_msgqueues(ch);
+                spin_lock_irqsave(&ch->lock, *irq_flags);
+
+                if (ret != xpcSuccess) {
+                        XPC_DISCONNECT_CHANNEL(ch, ret, irq_flags);
+                }
+                if (ch->flags & (XPC_C_CONNECTED | XPC_C_DISCONNECTING)) {
+                        return;
+                }
+
+                DBUG_ON(!(ch->flags & XPC_C_SETUP));
+                DBUG_ON(ch->local_msgqueue == NULL);
+                DBUG_ON(ch->remote_msgqueue == NULL);
+        }
+
+        if (!(ch->flags & XPC_C_OPENREPLY)) {
+                ch->flags |= XPC_C_OPENREPLY;
+                xpc_IPI_send_openreply(ch, irq_flags);
+        }
+
+        if (!(ch->flags & XPC_C_ROPENREPLY)) {
+                return;
+        }
+
+        DBUG_ON(ch->remote_msgqueue_pa == 0);
+
+        ch->flags = (XPC_C_CONNECTED | XPC_C_SETUP);    /* clear all else */
+
+        dev_info(xpc_chan, "channel %d to partition %d connected\n",
+                ch->number, ch->partid);
+
+        spin_unlock_irqrestore(&ch->lock, *irq_flags);
+        xpc_create_kthreads(ch, 1, 0);
+        spin_lock_irqsave(&ch->lock, *irq_flags);
+}
+
+
+/*
+ * Notify those who wanted to be notified upon delivery of their message.
+ */
+static void
+xpc_notify_senders(struct xpc_channel *ch, enum xpc_retval reason, s64 put)
+{
+        struct xpc_notify *notify;
+        u8 notify_type;
+        s64 get = ch->w_remote_GP.get - 1;
+
+
+        while (++get < put && atomic_read(&ch->n_to_notify) > 0) {
+
+                notify = &ch->notify_queue[get % ch->local_nentries];
+
+                /*
+                 * See if the notify entry indicates it was associated with
+                 * a message who's sender wants to be notified. It is possible
+                 * that it is, but someone else is doing or has done the
+                 * notification.
+                 */
+                notify_type = notify->type;
+                if (notify_type == 0 ||
+                                cmpxchg(&notify->type, notify_type, 0) !=
+                                                                notify_type) {
+                        continue;
+                }
+
+                DBUG_ON(notify_type != XPC_N_CALL);
+
+                atomic_dec(&ch->n_to_notify);
+
+                if (notify->func != NULL) {
+                        dev_dbg(xpc_chan, "notify->func() called, notify=0x%p, "
+                                "msg_number=%ld, partid=%d, channel=%d\n",
+                                (void *) notify, get, ch->partid, ch->number);
+
+                        notify->func(reason, ch->partid, ch->number,
+                                                                notify->key);
+
+                        dev_dbg(xpc_chan, "notify->func() returned, "
+                                "notify=0x%p, msg_number=%ld, partid=%d, "
+                                "channel=%d\n", (void *) notify, get,
+                                ch->partid, ch->number);
+                }
+        }
+}
+
+
+/*
+ * Free up message queues and other stuff that were allocated for the specified
+ * channel.
+ *
+ * Note: ch->reason and ch->reason_line are left set for debugging purposes,
+ * they're cleared when XPC_C_DISCONNECTED is cleared.
+ */
+static void
+xpc_free_msgqueues(struct xpc_channel *ch)
+{
+        DBUG_ON(!spin_is_locked(&ch->lock));
+        DBUG_ON(atomic_read(&ch->n_to_notify) != 0);
+
+        ch->remote_msgqueue_pa = 0;
+        ch->func = NULL;
+        ch->key = NULL;
+        ch->msg_size = 0;
+        ch->local_nentries = 0;
+        ch->remote_nentries = 0;
+        ch->kthreads_assigned_limit = 0;
+        ch->kthreads_idle_limit = 0;
+
+        ch->local_GP->get = 0;
+        ch->local_GP->put = 0;
+        ch->remote_GP.get = 0;
+        ch->remote_GP.put = 0;
+        ch->w_local_GP.get = 0;
+        ch->w_local_GP.put = 0;
+        ch->w_remote_GP.get = 0;
+        ch->w_remote_GP.put = 0;
+        ch->next_msg_to_pull = 0;
+
+        if (ch->flags & XPC_C_SETUP) {
+                ch->flags &= ~XPC_C_SETUP;
+
+                dev_dbg(xpc_chan, "ch->flags=0x%x, partid=%d, channel=%d\n",
+                        ch->flags, ch->partid, ch->number);
+
+                kfree(ch->local_msgqueue_base);
+                ch->local_msgqueue = NULL;
+                kfree(ch->remote_msgqueue_base);
+                ch->remote_msgqueue = NULL;
+                kfree(ch->notify_queue);
+                ch->notify_queue = NULL;
+        }
+}
+
+
+/*
+ * spin_lock_irqsave() is expected to be held on entry.
+ */
+static void
+xpc_process_disconnect(struct xpc_channel *ch, unsigned long *irq_flags)
+{
+        struct xpc_partition *part = &xpc_partitions[ch->partid];
+        u32 channel_was_connected = (ch->flags & XPC_C_WASCONNECTED);
+
+
+        DBUG_ON(!spin_is_locked(&ch->lock));
+
+        if (!(ch->flags & XPC_C_DISCONNECTING)) {
+                return;
+        }
+
+        DBUG_ON(!(ch->flags & XPC_C_CLOSEREQUEST));
+
+        /* make sure all activity has settled down first */
+
+        if (atomic_read(&ch->kthreads_assigned) > 0 ||
+                                atomic_read(&ch->references) > 0) {
+                return;
+        }
+        DBUG_ON((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+                        !(ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE));
+
+        if (part->act_state == XPC_P_DEACTIVATING) {
+                /* can't proceed until the other side disengages from us */
+                if (xpc_partition_engaged(1UL << ch->partid)) {
+                        return;
+                }
+
+        } else {
+
+                /* as long as the other side is up do the full protocol */
+
+                if (!(ch->flags & XPC_C_RCLOSEREQUEST)) {
+                        return;
+                }
+
+                if (!(ch->flags & XPC_C_CLOSEREPLY)) {
+                        ch->flags |= XPC_C_CLOSEREPLY;
+                        xpc_IPI_send_closereply(ch, irq_flags);
+                }
+
+                if (!(ch->flags & XPC_C_RCLOSEREPLY)) {
+                        return;
+                }
+        }
+
+        /* wake those waiting for notify completion */
+        if (atomic_read(&ch->n_to_notify) > 0) {
+                /* >>> we do callout while holding ch->lock */
+                xpc_notify_senders(ch, ch->reason, ch->w_local_GP.put);
+        }
+
+        /* both sides are disconnected now */
+
+        if (ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE) {
+                spin_unlock_irqrestore(&ch->lock, *irq_flags);
+                xpc_disconnect_callout(ch, xpcDisconnected);
+                spin_lock_irqsave(&ch->lock, *irq_flags);
+        }
+
+        /* it's now safe to free the channel's message queues */
+        xpc_free_msgqueues(ch);
+
+        /* mark disconnected, clear all other flags except XPC_C_WDISCONNECT */
+        ch->flags = (XPC_C_DISCONNECTED | (ch->flags & XPC_C_WDISCONNECT));
+
+        atomic_dec(&part->nchannels_active);
+
+        if (channel_was_connected) {
+                dev_info(xpc_chan, "channel %d to partition %d disconnected, "
+                        "reason=%d\n", ch->number, ch->partid, ch->reason);
+        }
+
+        if (ch->flags & XPC_C_WDISCONNECT) {
+                /* we won't lose the CPU since we're holding ch->lock */
+                complete(&ch->wdisconnect_wait);
+        } else if (ch->delayed_IPI_flags) {
+                if (part->act_state != XPC_P_DEACTIVATING) {
+                        /* time to take action on any delayed IPI flags */
+                        spin_lock(&part->IPI_lock);
+                        XPC_SET_IPI_FLAGS(part->local_IPI_amo, ch->number,
+                                                        ch->delayed_IPI_flags);
+                        spin_unlock(&part->IPI_lock);
+                }
+                ch->delayed_IPI_flags = 0;
+        }
+}
+
+
+/*
+ * Process a change in the channel's remote connection state.
+ */
+static void
+xpc_process_openclose_IPI(struct xpc_partition *part, int ch_number,
+                                u8 IPI_flags)
+{
+        unsigned long irq_flags;
+        struct xpc_openclose_args *args =
+                                &part->remote_openclose_args[ch_number];
+        struct xpc_channel *ch = &part->channels[ch_number];
+        enum xpc_retval reason;
+
+
+
+        spin_lock_irqsave(&ch->lock, irq_flags);
+
+again:
+
+        if ((ch->flags & XPC_C_DISCONNECTED) &&
+                                        (ch->flags & XPC_C_WDISCONNECT)) {
+                /*
+                 * Delay processing IPI flags until thread waiting disconnect
+                 * has had a chance to see that the channel is disconnected.
+                 */
+                ch->delayed_IPI_flags |= IPI_flags;
+                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                return;
+        }
+
+
+        if (IPI_flags & XPC_IPI_CLOSEREQUEST) {
+
+                dev_dbg(xpc_chan, "XPC_IPI_CLOSEREQUEST (reason=%d) received "
+                        "from partid=%d, channel=%d\n", args->reason,
+                        ch->partid, ch->number);
+
+                /*
+                 * If RCLOSEREQUEST is set, we're probably waiting for
+                 * RCLOSEREPLY. We should find it and a ROPENREQUEST packed
+                 * with this RCLOSEREQUEST in the IPI_flags.
+                 */
+
+                if (ch->flags & XPC_C_RCLOSEREQUEST) {
+                        DBUG_ON(!(ch->flags & XPC_C_DISCONNECTING));
+                        DBUG_ON(!(ch->flags & XPC_C_CLOSEREQUEST));
+                        DBUG_ON(!(ch->flags & XPC_C_CLOSEREPLY));
+                        DBUG_ON(ch->flags & XPC_C_RCLOSEREPLY);
+
+                        DBUG_ON(!(IPI_flags & XPC_IPI_CLOSEREPLY));
+                        IPI_flags &= ~XPC_IPI_CLOSEREPLY;
+                        ch->flags |= XPC_C_RCLOSEREPLY;
+
+                        /* both sides have finished disconnecting */
+                        xpc_process_disconnect(ch, &irq_flags);
+                        DBUG_ON(!(ch->flags & XPC_C_DISCONNECTED));
+                        goto again;
+                }
+
+                if (ch->flags & XPC_C_DISCONNECTED) {
+                        if (!(IPI_flags & XPC_IPI_OPENREQUEST)) {
+                                if ((XPC_GET_IPI_FLAGS(part->local_IPI_amo,
+                                         ch_number) & XPC_IPI_OPENREQUEST)) {
+
+                                        DBUG_ON(ch->delayed_IPI_flags != 0);
+                                        spin_lock(&part->IPI_lock);
+                                        XPC_SET_IPI_FLAGS(part->local_IPI_amo,
+                                                        ch_number,
+                                                        XPC_IPI_CLOSEREQUEST);
+                                        spin_unlock(&part->IPI_lock);
+                                }
+                                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                                return;
+                        }
+
+                        XPC_SET_REASON(ch, 0, 0);
+                        ch->flags &= ~XPC_C_DISCONNECTED;
+
+                        atomic_inc(&part->nchannels_active);
+                        ch->flags |= (XPC_C_CONNECTING | XPC_C_ROPENREQUEST);
+                }
+
+                IPI_flags &= ~(XPC_IPI_OPENREQUEST | XPC_IPI_OPENREPLY);
+
+                /*
+                 * The meaningful CLOSEREQUEST connection state fields are:
+                 *      reason = reason connection is to be closed
+                 */
+
+                ch->flags |= XPC_C_RCLOSEREQUEST;
+
+                if (!(ch->flags & XPC_C_DISCONNECTING)) {
+                        reason = args->reason;
+                        if (reason <= xpcSuccess || reason > xpcUnknownReason) {
+                                reason = xpcUnknownReason;
+                        } else if (reason == xpcUnregistering) {
+                                reason = xpcOtherUnregistering;
+                        }
+
+                        XPC_DISCONNECT_CHANNEL(ch, reason, &irq_flags);
+
+                        DBUG_ON(IPI_flags & XPC_IPI_CLOSEREPLY);
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+
+                xpc_process_disconnect(ch, &irq_flags);
+        }
+
+
+        if (IPI_flags & XPC_IPI_CLOSEREPLY) {
+
+                dev_dbg(xpc_chan, "XPC_IPI_CLOSEREPLY received from partid=%d,"
+                        " channel=%d\n", ch->partid, ch->number);
+
+                if (ch->flags & XPC_C_DISCONNECTED) {
+                        DBUG_ON(part->act_state != XPC_P_DEACTIVATING);
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+
+                DBUG_ON(!(ch->flags & XPC_C_CLOSEREQUEST));
+
+                if (!(ch->flags & XPC_C_RCLOSEREQUEST)) {
+                        if ((XPC_GET_IPI_FLAGS(part->local_IPI_amo, ch_number)
+                                                & XPC_IPI_CLOSEREQUEST)) {
+
+                                DBUG_ON(ch->delayed_IPI_flags != 0);
+                                spin_lock(&part->IPI_lock);
+                                XPC_SET_IPI_FLAGS(part->local_IPI_amo,
+                                                ch_number, XPC_IPI_CLOSEREPLY);
+                                spin_unlock(&part->IPI_lock);
+                        }
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+
+                ch->flags |= XPC_C_RCLOSEREPLY;
+
+                if (ch->flags & XPC_C_CLOSEREPLY) {
+                        /* both sides have finished disconnecting */
+                        xpc_process_disconnect(ch, &irq_flags);
+                }
+        }
+
+
+        if (IPI_flags & XPC_IPI_OPENREQUEST) {
+
+                dev_dbg(xpc_chan, "XPC_IPI_OPENREQUEST (msg_size=%d, "
+                        "local_nentries=%d) received from partid=%d, "
+                        "channel=%d\n", args->msg_size, args->local_nentries,
+                        ch->partid, ch->number);
+
+                if (part->act_state == XPC_P_DEACTIVATING ||
+                                        (ch->flags & XPC_C_ROPENREQUEST)) {
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+
+                if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_WDISCONNECT)) {
+                        ch->delayed_IPI_flags |= XPC_IPI_OPENREQUEST;
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+                DBUG_ON(!(ch->flags & (XPC_C_DISCONNECTED |
+                                                        XPC_C_OPENREQUEST)));
+                DBUG_ON(ch->flags & (XPC_C_ROPENREQUEST | XPC_C_ROPENREPLY |
+                                        XPC_C_OPENREPLY | XPC_C_CONNECTED));
+
+                /*
+                 * The meaningful OPENREQUEST connection state fields are:
+                 *      msg_size = size of channel's messages in bytes
+                 *      local_nentries = remote partition's local_nentries
+                 */
+                if (args->msg_size == 0 || args->local_nentries == 0) {
+                        /* assume OPENREQUEST was delayed by mistake */
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+
+                ch->flags |= (XPC_C_ROPENREQUEST | XPC_C_CONNECTING);
+                ch->remote_nentries = args->local_nentries;
+
+
+                if (ch->flags & XPC_C_OPENREQUEST) {
+                        if (args->msg_size != ch->msg_size) {
+                                XPC_DISCONNECT_CHANNEL(ch, xpcUnequalMsgSizes,
+                                                                &irq_flags);
+                                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                                return;
+                        }
+                } else {
+                        ch->msg_size = args->msg_size;
+
+                        XPC_SET_REASON(ch, 0, 0);
+                        ch->flags &= ~XPC_C_DISCONNECTED;
+
+                        atomic_inc(&part->nchannels_active);
+                }
+
+                xpc_process_connect(ch, &irq_flags);
+        }
+
+
+        if (IPI_flags & XPC_IPI_OPENREPLY) {
+
+                dev_dbg(xpc_chan, "XPC_IPI_OPENREPLY (local_msgqueue_pa=0x%lx, "
+                        "local_nentries=%d, remote_nentries=%d) received from "
+                        "partid=%d, channel=%d\n", args->local_msgqueue_pa,
+                        args->local_nentries, args->remote_nentries,
+                        ch->partid, ch->number);
+
+                if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_DISCONNECTED)) {
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+                if (!(ch->flags & XPC_C_OPENREQUEST)) {
+                        XPC_DISCONNECT_CHANNEL(ch, xpcOpenCloseError,
+                                                                &irq_flags);
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return;
+                }
+
+                DBUG_ON(!(ch->flags & XPC_C_ROPENREQUEST));
+                DBUG_ON(ch->flags & XPC_C_CONNECTED);
+
+                /*
+                 * The meaningful OPENREPLY connection state fields are:
+                 *      local_msgqueue_pa = physical address of remote
+                 *                          partition's local_msgqueue
+                 *      local_nentries = remote partition's local_nentries
+                 *      remote_nentries = remote partition's remote_nentries
+                 */
+                DBUG_ON(args->local_msgqueue_pa == 0);
+                DBUG_ON(args->local_nentries == 0);
+                DBUG_ON(args->remote_nentries == 0);
+
+                ch->flags |= XPC_C_ROPENREPLY;
+                ch->remote_msgqueue_pa = args->local_msgqueue_pa;
+
+                if (args->local_nentries < ch->remote_nentries) {
+                        dev_dbg(xpc_chan, "XPC_IPI_OPENREPLY: new "
+                                "remote_nentries=%d, old remote_nentries=%d, "
+                                "partid=%d, channel=%d\n",
+                                args->local_nentries, ch->remote_nentries,
+                                ch->partid, ch->number);
+
+                        ch->remote_nentries = args->local_nentries;
+                }
+                if (args->remote_nentries < ch->local_nentries) {
+                        dev_dbg(xpc_chan, "XPC_IPI_OPENREPLY: new "
+                                "local_nentries=%d, old local_nentries=%d, "
+                                "partid=%d, channel=%d\n",
+                                args->remote_nentries, ch->local_nentries,
+                                ch->partid, ch->number);
+
+                        ch->local_nentries = args->remote_nentries;
+                }
+
+                xpc_process_connect(ch, &irq_flags);
+        }
+
+        spin_unlock_irqrestore(&ch->lock, irq_flags);
+}
+
+
+/*
+ * Attempt to establish a channel connection to a remote partition.
+ */
+static enum xpc_retval
+xpc_connect_channel(struct xpc_channel *ch)
+{
+        unsigned long irq_flags;
+        struct xpc_registration *registration = &xpc_registrations[ch->number];
+
+
+        if (mutex_trylock(&registration->mutex) == 0) {
+                return xpcRetry;
+        }
+
+        if (!XPC_CHANNEL_REGISTERED(ch->number)) {
+                mutex_unlock(&registration->mutex);
+                return xpcUnregistered;
+        }
+
+        spin_lock_irqsave(&ch->lock, irq_flags);
+
+        DBUG_ON(ch->flags & XPC_C_CONNECTED);
+        DBUG_ON(ch->flags & XPC_C_OPENREQUEST);
+
+        if (ch->flags & XPC_C_DISCONNECTING) {
+                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                mutex_unlock(&registration->mutex);
+                return ch->reason;
+        }
+
+
+        /* add info from the channel connect registration to the channel */
+
+        ch->kthreads_assigned_limit = registration->assigned_limit;
+        ch->kthreads_idle_limit = registration->idle_limit;
+        DBUG_ON(atomic_read(&ch->kthreads_assigned) != 0);
+        DBUG_ON(atomic_read(&ch->kthreads_idle) != 0);
+        DBUG_ON(atomic_read(&ch->kthreads_active) != 0);
+
+        ch->func = registration->func;
+        DBUG_ON(registration->func == NULL);
+        ch->key = registration->key;
+
+        ch->local_nentries = registration->nentries;
+
+        if (ch->flags & XPC_C_ROPENREQUEST) {
+                if (registration->msg_size != ch->msg_size) {
+                        /* the local and remote sides aren't the same */
+
+                        /*
+                         * Because XPC_DISCONNECT_CHANNEL() can block we're
+                         * forced to up the registration sema before we unlock
+                         * the channel lock. But that's okay here because we're
+                         * done with the part that required the registration
+                         * sema. XPC_DISCONNECT_CHANNEL() requires that the
+                         * channel lock be locked and will unlock and relock
+                         * the channel lock as needed.
+                         */
+                        mutex_unlock(&registration->mutex);
+                        XPC_DISCONNECT_CHANNEL(ch, xpcUnequalMsgSizes,
+                                                                &irq_flags);
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        return xpcUnequalMsgSizes;
+                }
+        } else {
+                ch->msg_size = registration->msg_size;
+
+                XPC_SET_REASON(ch, 0, 0);
+                ch->flags &= ~XPC_C_DISCONNECTED;
+
+                atomic_inc(&xpc_partitions[ch->partid].nchannels_active);
+        }
+
+        mutex_unlock(&registration->mutex);
+
+
+        /* initiate the connection */
+
+        ch->flags |= (XPC_C_OPENREQUEST | XPC_C_CONNECTING);
+        xpc_IPI_send_openrequest(ch, &irq_flags);
+
+        xpc_process_connect(ch, &irq_flags);
+
+        spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+        return xpcSuccess;
+}
+
+
+/*
+ * Clear some of the msg flags in the local message queue.
+ */
+static inline void
+xpc_clear_local_msgqueue_flags(struct xpc_channel *ch)
+{
+        struct xpc_msg *msg;
+        s64 get;
+
+
+        get = ch->w_remote_GP.get;
+        do {
+                msg = (struct xpc_msg *) ((u64) ch->local_msgqueue +
+                                (get % ch->local_nentries) * ch->msg_size);
+                msg->flags = 0;
+        } while (++get < (volatile s64) ch->remote_GP.get);
+}
+
+
+/*
+ * Clear some of the msg flags in the remote message queue.
+ */
+static inline void
+xpc_clear_remote_msgqueue_flags(struct xpc_channel *ch)
+{
+        struct xpc_msg *msg;
+        s64 put;
+
+
+        put = ch->w_remote_GP.put;
+        do {
+                msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue +
+                                (put % ch->remote_nentries) * ch->msg_size);
+                msg->flags = 0;
+        } while (++put < (volatile s64) ch->remote_GP.put);
+}
+
+
+static void
+xpc_process_msg_IPI(struct xpc_partition *part, int ch_number)
+{
+        struct xpc_channel *ch = &part->channels[ch_number];
+        int nmsgs_sent;
+
+
+        ch->remote_GP = part->remote_GPs[ch_number];
+
+
+        /* See what, if anything, has changed for each connected channel */
+
+        xpc_msgqueue_ref(ch);
+
+        if (ch->w_remote_GP.get == ch->remote_GP.get &&
+                                ch->w_remote_GP.put == ch->remote_GP.put) {
+                /* nothing changed since GPs were last pulled */
+                xpc_msgqueue_deref(ch);
+                return;
+        }
+
+        if (!(ch->flags & XPC_C_CONNECTED)){
+                xpc_msgqueue_deref(ch);
+                return;
+        }
+
+
+        /*
+         * First check to see if messages recently sent by us have been
+         * received by the other side. (The remote GET value will have
+         * changed since we last looked at it.)
+         */
+
+        if (ch->w_remote_GP.get != ch->remote_GP.get) {
+
+                /*
+                 * We need to notify any senders that want to be notified
+                 * that their sent messages have been received by their
+                 * intended recipients. We need to do this before updating
+                 * w_remote_GP.get so that we don't allocate the same message
+                 * queue entries prematurely (see xpc_allocate_msg()).
+                 */
+                if (atomic_read(&ch->n_to_notify) > 0) {
+                        /*
+                         * Notify senders that messages sent have been
+                         * received and delivered by the other side.
+                         */
+                        xpc_notify_senders(ch, xpcMsgDelivered,
+                                                        ch->remote_GP.get);
+                }
+
+                /*
+                 * Clear msg->flags in previously sent messages, so that
+                 * they're ready for xpc_allocate_msg().
+                 */
+                xpc_clear_local_msgqueue_flags(ch);
+
+                ch->w_remote_GP.get = ch->remote_GP.get;
+
+                dev_dbg(xpc_chan, "w_remote_GP.get changed to %ld, partid=%d, "
+                        "channel=%d\n", ch->w_remote_GP.get, ch->partid,
+                        ch->number);
+
+                /*
+                 * If anyone was waiting for message queue entries to become
+                 * available, wake them up.
+                 */
+                if (atomic_read(&ch->n_on_msg_allocate_wq) > 0) {
+                        wake_up(&ch->msg_allocate_wq);
+                }
+        }
+
+
+        /*
+         * Now check for newly sent messages by the other side. (The remote
+         * PUT value will have changed since we last looked at it.)
+         */
+
+        if (ch->w_remote_GP.put != ch->remote_GP.put) {
+                /*
+                 * Clear msg->flags in previously received messages, so that
+                 * they're ready for xpc_get_deliverable_msg().
+                 */
+                xpc_clear_remote_msgqueue_flags(ch);
+
+                ch->w_remote_GP.put = ch->remote_GP.put;
+
+                dev_dbg(xpc_chan, "w_remote_GP.put changed to %ld, partid=%d, "
+                        "channel=%d\n", ch->w_remote_GP.put, ch->partid,
+                        ch->number);
+
+                nmsgs_sent = ch->w_remote_GP.put - ch->w_local_GP.get;
+                if (nmsgs_sent > 0) {
+                        dev_dbg(xpc_chan, "msgs waiting to be copied and "
+                                "delivered=%d, partid=%d, channel=%d\n",
+                                nmsgs_sent, ch->partid, ch->number);
+
+                        if (ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) {
+                                xpc_activate_kthreads(ch, nmsgs_sent);
+                        }
+                }
+        }
+
+        xpc_msgqueue_deref(ch);
+}
+
+
+void
+xpc_process_channel_activity(struct xpc_partition *part)
+{
+        unsigned long irq_flags;
+        u64 IPI_amo, IPI_flags;
+        struct xpc_channel *ch;
+        int ch_number;
+        u32 ch_flags;
+
+
+        IPI_amo = xpc_get_IPI_flags(part);
+
+        /*
+         * Initiate channel connections for registered channels.
+         *
+         * For each connected channel that has pending messages activate idle
+         * kthreads and/or create new kthreads as needed.
+         */
+
+        for (ch_number = 0; ch_number < part->nchannels; ch_number++) {
+                ch = &part->channels[ch_number];
+
+
+                /*
+                 * Process any open or close related IPI flags, and then deal
+                 * with connecting or disconnecting the channel as required.
+                 */
+
+                IPI_flags = XPC_GET_IPI_FLAGS(IPI_amo, ch_number);
+
+                if (XPC_ANY_OPENCLOSE_IPI_FLAGS_SET(IPI_flags)) {
+                        xpc_process_openclose_IPI(part, ch_number, IPI_flags);
+                }
+
+                ch_flags = ch->flags;   /* need an atomic snapshot of flags */
+
+                if (ch_flags & XPC_C_DISCONNECTING) {
+                        spin_lock_irqsave(&ch->lock, irq_flags);
+                        xpc_process_disconnect(ch, &irq_flags);
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        continue;
+                }
+
+                if (part->act_state == XPC_P_DEACTIVATING) {
+                        continue;
+                }
+
+                if (!(ch_flags & XPC_C_CONNECTED)) {
+                        if (!(ch_flags & XPC_C_OPENREQUEST)) {
+                                DBUG_ON(ch_flags & XPC_C_SETUP);
+                                (void) xpc_connect_channel(ch);
+                        } else {
+                                spin_lock_irqsave(&ch->lock, irq_flags);
+                                xpc_process_connect(ch, &irq_flags);
+                                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                        }
+                        continue;
+                }
+
+
+                /*
+                 * Process any message related IPI flags, this may involve the
+                 * activation of kthreads to deliver any pending messages sent
+                 * from the other partition.
+                 */
+
+                if (XPC_ANY_MSG_IPI_FLAGS_SET(IPI_flags)) {
+                        xpc_process_msg_IPI(part, ch_number);
+                }
+        }
+}
+
+
+/*
+ * XPC's heartbeat code calls this function to inform XPC that a partition is
+ * going down.  XPC responds by tearing down the XPartition Communication
+ * infrastructure used for the just downed partition.
+ *
+ * XPC's heartbeat code will never call this function and xpc_partition_up()
+ * at the same time. Nor will it ever make multiple calls to either function
+ * at the same time.
+ */
+void
+xpc_partition_going_down(struct xpc_partition *part, enum xpc_retval reason)
+{
+        unsigned long irq_flags;
+        int ch_number;
+        struct xpc_channel *ch;
+
+
+        dev_dbg(xpc_chan, "deactivating partition %d, reason=%d\n",
+                XPC_PARTID(part), reason);
+
+        if (!xpc_part_ref(part)) {
+                /* infrastructure for this partition isn't currently set up */
+                return;
+        }
+
+
+        /* disconnect channels associated with the partition going down */
+
+        for (ch_number = 0; ch_number < part->nchannels; ch_number++) {
+                ch = &part->channels[ch_number];
+
+                xpc_msgqueue_ref(ch);
+                spin_lock_irqsave(&ch->lock, irq_flags);
+
+                XPC_DISCONNECT_CHANNEL(ch, reason, &irq_flags);
+
+                spin_unlock_irqrestore(&ch->lock, irq_flags);
+                xpc_msgqueue_deref(ch);
+        }
+
+        xpc_wakeup_channel_mgr(part);
+
+        xpc_part_deref(part);
+}
+
+
+/*
+ * Teardown the infrastructure necessary to support XPartition Communication
+ * between the specified remote partition and the local one.
+ */
+void
+xpc_teardown_infrastructure(struct xpc_partition *part)
+{
+        partid_t partid = XPC_PARTID(part);
+
+
+        /*
+         * We start off by making this partition inaccessible to local
+         * processes by marking it as no longer setup. Then we make it
+         * inaccessible to remote processes by clearing the XPC per partition
+         * specific variable's magic # (which indicates that these variables
+         * are no longer valid) and by ignoring all XPC notify IPIs sent to
+         * this partition.
+         */
+
+        DBUG_ON(atomic_read(&part->nchannels_engaged) != 0);
+        DBUG_ON(atomic_read(&part->nchannels_active) != 0);
+        DBUG_ON(part->setup_state != XPC_P_SETUP);
+        part->setup_state = XPC_P_WTEARDOWN;
+
+        xpc_vars_part[partid].magic = 0;
+
+
+        free_irq(SGI_XPC_NOTIFY, (void *) (u64) partid);
+
+
+        /*
+         * Before proceeding with the teardown we have to wait until all
+         * existing references cease.
+         */
+        wait_event(part->teardown_wq, (atomic_read(&part->references) == 0));
+
+
+        /* now we can begin tearing down the infrastructure */
+
+        part->setup_state = XPC_P_TORNDOWN;
+
+        /* in case we've still got outstanding timers registered... */
+        del_timer_sync(&part->dropped_IPI_timer);
+
+        kfree(part->remote_openclose_args_base);
+        part->remote_openclose_args = NULL;
+        kfree(part->local_openclose_args_base);
+        part->local_openclose_args = NULL;
+        kfree(part->remote_GPs_base);
+        part->remote_GPs = NULL;
+        kfree(part->local_GPs_base);
+        part->local_GPs = NULL;
+        kfree(part->channels);
+        part->channels = NULL;
+        part->local_IPI_amo_va = NULL;
+}
+
+
+/*
+ * Called by XP at the time of channel connection registration to cause
+ * XPC to establish connections to all currently active partitions.
+ */
+void
+xpc_initiate_connect(int ch_number)
+{
+        partid_t partid;
+        struct xpc_partition *part;
+        struct xpc_channel *ch;
+
+
+        DBUG_ON(ch_number < 0 || ch_number >= XPC_NCHANNELS);
+
+        for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
+                part = &xpc_partitions[partid];
+
+                if (xpc_part_ref(part)) {
+                        ch = &part->channels[ch_number];
+
+                        /*
+                         * Initiate the establishment of a connection on the
+                         * newly registered channel to the remote partition.
+                         */
+                        xpc_wakeup_channel_mgr(part);
+                        xpc_part_deref(part);
+                }
+        }
+}
+
+
+void
+xpc_connected_callout(struct xpc_channel *ch)
+{
+        /* let the registerer know that a connection has been established */
+
+        if (ch->func != NULL) {
+                dev_dbg(xpc_chan, "ch->func() called, reason=xpcConnected, "
+                        "partid=%d, channel=%d\n", ch->partid, ch->number);
+
+                ch->func(xpcConnected, ch->partid, ch->number,
+                                (void *) (u64) ch->local_nentries, ch->key);
+
+                dev_dbg(xpc_chan, "ch->func() returned, reason=xpcConnected, "
+                        "partid=%d, channel=%d\n", ch->partid, ch->number);
+        }
+}
+
+
+/*
+ * Called by XP at the time of channel connection unregistration to cause
+ * XPC to teardown all current connections for the specified channel.
+ *
+ * Before returning xpc_initiate_disconnect() will wait until all connections
+ * on the specified channel have been closed/torndown. So the caller can be
+ * assured that they will not be receiving any more callouts from XPC to the
+ * function they registered via xpc_connect().
+ *
+ * Arguments:
+ *
+ *      ch_number - channel # to unregister.
+ */
+void
+xpc_initiate_disconnect(int ch_number)
+{
+        unsigned long irq_flags;
+        partid_t partid;
+        struct xpc_partition *part;
+        struct xpc_channel *ch;
+
+
+        DBUG_ON(ch_number < 0 || ch_number >= XPC_NCHANNELS);
+
+        /* initiate the channel disconnect for every active partition */
+        for (partid = 1; partid < XP_MAX_PARTITIONS; partid++) {
+                part = &xpc_partitions[partid];
+
+                if (xpc_part_ref(part)) {
+                        ch = &part->channels[ch_number];
+                        xpc_msgqueue_ref(ch);
+
+                        spin_lock_irqsave(&ch->lock, irq_flags);
+
+                        if (!(ch->flags & XPC_C_DISCONNECTED)) {
+                                ch->flags |= XPC_C_WDISCONNECT;
+
+                                XPC_DISCONNECT_CHANNEL(ch, xpcUnregistering,
+                                                                &irq_flags);
+                        }
+
+                        spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+                        xpc_msgqueue_deref(ch);
+                        xpc_part_deref(part);
+                }
+        }
+
+        xpc_disconnect_wait(ch_number);
+}
+
+
+/*
+ * To disconnect a channel, and reflect it back to all who may be waiting.
+ *
+ * An OPEN is not allowed until XPC_C_DISCONNECTING is cleared by
+ * xpc_process_disconnect(), and if set, XPC_C_WDISCONNECT is cleared by
+ * xpc_disconnect_wait().
+ *
+ * THE CHANNEL IS TO BE LOCKED BY THE CALLER AND WILL REMAIN LOCKED UPON RETURN.
+ */
+void
+xpc_disconnect_channel(const int line, struct xpc_channel *ch,
+                        enum xpc_retval reason, unsigned long *irq_flags)
+{
+        u32 channel_was_connected = (ch->flags & XPC_C_CONNECTED);
+
+
+        DBUG_ON(!spin_is_locked(&ch->lock));
+
+        if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_DISCONNECTED)) {
+                return;
+        }
+        DBUG_ON(!(ch->flags & (XPC_C_CONNECTING | XPC_C_CONNECTED)));
+
+        dev_dbg(xpc_chan, "reason=%d, line=%d, partid=%d, channel=%d\n",
+                reason, line, ch->partid, ch->number);
+
+        XPC_SET_REASON(ch, reason, line);
+
+        ch->flags |= (XPC_C_CLOSEREQUEST | XPC_C_DISCONNECTING);
+        /* some of these may not have been set */
+        ch->flags &= ~(XPC_C_OPENREQUEST | XPC_C_OPENREPLY |
+                        XPC_C_ROPENREQUEST | XPC_C_ROPENREPLY |
+                        XPC_C_CONNECTING | XPC_C_CONNECTED);
+
+        xpc_IPI_send_closerequest(ch, irq_flags);
+
+        if (channel_was_connected) {
+                ch->flags |= XPC_C_WASCONNECTED;
+        }
+
+        spin_unlock_irqrestore(&ch->lock, *irq_flags);
+
+        /* wake all idle kthreads so they can exit */
+        if (atomic_read(&ch->kthreads_idle) > 0) {
+                wake_up_all(&ch->idle_wq);
+
+        } else if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+                        !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
+                /* start a kthread that will do the xpcDisconnecting callout */
+                xpc_create_kthreads(ch, 1, 1);
+        }
+
+        /* wake those waiting to allocate an entry from the local msg queue */
+        if (atomic_read(&ch->n_on_msg_allocate_wq) > 0) {
+                wake_up(&ch->msg_allocate_wq);
+        }
+
+        spin_lock_irqsave(&ch->lock, *irq_flags);
+}
+
+
+void
+xpc_disconnect_callout(struct xpc_channel *ch, enum xpc_retval reason)
+{
+        /*
+         * Let the channel's registerer know that the channel is being
+         * disconnected. We don't want to do this if the registerer was never
+         * informed of a connection being made.
+         */
+
+        if (ch->func != NULL) {
+                dev_dbg(xpc_chan, "ch->func() called, reason=%d, partid=%d, "
+                        "channel=%d\n", reason, ch->partid, ch->number);
+
+                ch->func(reason, ch->partid, ch->number, NULL, ch->key);
+
+                dev_dbg(xpc_chan, "ch->func() returned, reason=%d, partid=%d, "
+                        "channel=%d\n", reason, ch->partid, ch->number);
+        }
+}
+
+
+/*
+ * Wait for a message entry to become available for the specified channel,
+ * but don't wait any longer than 1 jiffy.
+ */
+static enum xpc_retval
+xpc_allocate_msg_wait(struct xpc_channel *ch)
+{
+        enum xpc_retval ret;
+
+
+        if (ch->flags & XPC_C_DISCONNECTING) {
+                DBUG_ON(ch->reason == xpcInterrupted);  // >>> Is this true?
+                return ch->reason;
+        }
+
+        atomic_inc(&ch->n_on_msg_allocate_wq);
+        ret = interruptible_sleep_on_timeout(&ch->msg_allocate_wq, 1);
+        atomic_dec(&ch->n_on_msg_allocate_wq);
+
+        if (ch->flags & XPC_C_DISCONNECTING) {
+                ret = ch->reason;
+                DBUG_ON(ch->reason == xpcInterrupted);  // >>> Is this true?
+        } else if (ret == 0) {
+                ret = xpcTimeout;
+        } else {
+                ret = xpcInterrupted;
+        }
+
+        return ret;
+}
+
+
+/*
+ * Allocate an entry for a message from the message queue associated with the
+ * specified channel.
+ */
+static enum xpc_retval
+xpc_allocate_msg(struct xpc_channel *ch, u32 flags,
+                        struct xpc_msg **address_of_msg)
+{
+        struct xpc_msg *msg;
+        enum xpc_retval ret;
+        s64 put;
+
+
+        /* this reference will be dropped in xpc_send_msg() */
+        xpc_msgqueue_ref(ch);
+
+        if (ch->flags & XPC_C_DISCONNECTING) {
+                xpc_msgqueue_deref(ch);
+                return ch->reason;
+        }
+        if (!(ch->flags & XPC_C_CONNECTED)) {
+                xpc_msgqueue_deref(ch);
+                return xpcNotConnected;
+        }
+
+
+        /*
+         * Get the next available message entry from the local message queue.
+         * If none are available, we'll make sure that we grab the latest
+         * GP values.
+         */
+        ret = xpcTimeout;
+
+        while (1) {
+
+                put = (volatile s64) ch->w_local_GP.put;
+                if (put - (volatile s64) ch->w_remote_GP.get <
+                                                        ch->local_nentries) {
+
+                        /* There are available message entries. We need to try
+                         * to secure one for ourselves. We'll do this by trying
+                         * to increment w_local_GP.put as long as someone else
+                         * doesn't beat us to it. If they do, we'll have to
+                         * try again.
+                         */
+                        if (cmpxchg(&ch->w_local_GP.put, put, put + 1) ==
+                                                                        put) {
+                                /* we got the entry referenced by put */
+                                break;
+                        }
+                        continue;       /* try again */
+                }
+
+
+                /*
+                 * There aren't any available msg entries at this time.
+                 *
+                 * In waiting for a message entry to become available,
+                 * we set a timeout in case the other side is not
+                 * sending completion IPIs. This lets us fake an IPI
+                 * that will cause the IPI handler to fetch the latest
+                 * GP values as if an IPI was sent by the other side.
+                 */
+                if (ret == xpcTimeout) {
+                        xpc_IPI_send_local_msgrequest(ch);
+                }
+
+                if (flags & XPC_NOWAIT) {
+                        xpc_msgqueue_deref(ch);
+                        return xpcNoWait;
+                }
+
+                ret = xpc_allocate_msg_wait(ch);
+                if (ret != xpcInterrupted && ret != xpcTimeout) {
+                        xpc_msgqueue_deref(ch);
+                        return ret;
+                }
+        }
+
+
+        /* get the message's address and initialize it */
+        msg = (struct xpc_msg *) ((u64) ch->local_msgqueue +
+                                (put % ch->local_nentries) * ch->msg_size);
+
+
+        DBUG_ON(msg->flags != 0);
+        msg->number = put;
+
+        dev_dbg(xpc_chan, "w_local_GP.put changed to %ld; msg=0x%p, "
+                "msg_number=%ld, partid=%d, channel=%d\n", put + 1,
+                (void *) msg, msg->number, ch->partid, ch->number);
+
+        *address_of_msg = msg;
+
+        return xpcSuccess;
+}
+
+
+/*
+ * Allocate an entry for a message from the message queue associated with the
+ * specified channel. NOTE that this routine can sleep waiting for a message
+ * entry to become available. To not sleep, pass in the XPC_NOWAIT flag.
+ *
+ * Arguments:
+ *
+ *      partid - ID of partition to which the channel is connected.
+ *      ch_number - channel #.
+ *      flags - see xpc.h for valid flags.
+ *      payload - address of the allocated payload area pointer (filled in on
+ *                return) in which the user-defined message is constructed.
+ */
+enum xpc_retval
+xpc_initiate_allocate(partid_t partid, int ch_number, u32 flags, void **payload)
+{
+        struct xpc_partition *part = &xpc_partitions[partid];
+        enum xpc_retval ret = xpcUnknownReason;
+        struct xpc_msg *msg = NULL;
+
+
+        DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
+        DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
+
+        *payload = NULL;
+
+        if (xpc_part_ref(part)) {
+                ret = xpc_allocate_msg(&part->channels[ch_number], flags, &msg);
+                xpc_part_deref(part);
+
+                if (msg != NULL) {
+                        *payload = &msg->payload;
+                }
+        }
+
+        return ret;
+}
+
+
+/*
+ * Now we actually send the messages that are ready to be sent by advancing
+ * the local message queue's Put value and then send an IPI to the recipient
+ * partition.
+ */
+static void
+xpc_send_msgs(struct xpc_channel *ch, s64 initial_put)
+{
+        struct xpc_msg *msg;
+        s64 put = initial_put + 1;
+        int send_IPI = 0;
+
+
+        while (1) {
+
+                while (1) {
+                        if (put == (volatile s64) ch->w_local_GP.put) {
+                                break;
+                        }
+
+                        msg = (struct xpc_msg *) ((u64) ch->local_msgqueue +
+                               (put % ch->local_nentries) * ch->msg_size);
+
+                        if (!(msg->flags & XPC_M_READY)) {
+                                break;
+                        }
+
+                        put++;
+                }
+
+                if (put == initial_put) {
+                        /* nothing's changed */
+                        break;
+                }
+
+                if (cmpxchg_rel(&ch->local_GP->put, initial_put, put) !=
+                                                                initial_put) {
+                        /* someone else beat us to it */
+                        DBUG_ON((volatile s64) ch->local_GP->put < initial_put);
+                        break;
+                }
+
+                /* we just set the new value of local_GP->put */
+
+                dev_dbg(xpc_chan, "local_GP->put changed to %ld, partid=%d, "
+                        "channel=%d\n", put, ch->partid, ch->number);
+
+                send_IPI = 1;
+
+                /*
+                 * We need to ensure that the message referenced by
+                 * local_GP->put is not XPC_M_READY or that local_GP->put
+                 * equals w_local_GP.put, so we'll go have a look.
+                 */
+                initial_put = put;
+        }
+
+        if (send_IPI) {
+                xpc_IPI_send_msgrequest(ch);
+        }
+}
+
+
+/*
+ * Common code that does the actual sending of the message by advancing the
+ * local message queue's Put value and sends an IPI to the partition the
+ * message is being sent to.
+ */
+static enum xpc_retval
+xpc_send_msg(struct xpc_channel *ch, struct xpc_msg *msg, u8 notify_type,
+                        xpc_notify_func func, void *key)
+{
+        enum xpc_retval ret = xpcSuccess;
+        struct xpc_notify *notify = notify;
+        s64 put, msg_number = msg->number;
+
+
+        DBUG_ON(notify_type == XPC_N_CALL && func == NULL);
+        DBUG_ON((((u64) msg - (u64) ch->local_msgqueue) / ch->msg_size) !=
+                                        msg_number % ch->local_nentries);
+        DBUG_ON(msg->flags & XPC_M_READY);
+
+        if (ch->flags & XPC_C_DISCONNECTING) {
+                /* drop the reference grabbed in xpc_allocate_msg() */
+                xpc_msgqueue_deref(ch);
+                return ch->reason;
+        }
+
+        if (notify_type != 0) {
+                /*
+                 * Tell the remote side to send an ACK interrupt when the
+                 * message has been delivered.
+                 */
+                msg->flags |= XPC_M_INTERRUPT;
+
+                atomic_inc(&ch->n_to_notify);
+
+                notify = &ch->notify_queue[msg_number % ch->local_nentries];
+                notify->func = func;
+                notify->key = key;
+                notify->type = notify_type;
+
+                // >>> is a mb() needed here?
+
+                if (ch->flags & XPC_C_DISCONNECTING) {
+                        /*
+                         * An error occurred between our last error check and
+                         * this one. We will try to clear the type field from
+                         * the notify entry. If we succeed then
+                         * xpc_disconnect_channel() didn't already process
+                         * the notify entry.
+                         */
+                        if (cmpxchg(&notify->type, notify_type, 0) ==
+                                                                notify_type) {
+                                atomic_dec(&ch->n_to_notify);
+                                ret = ch->reason;
+                        }
+
+                        /* drop the reference grabbed in xpc_allocate_msg() */
+                        xpc_msgqueue_deref(ch);
+                        return ret;
+                }
+        }
+
+        msg->flags |= XPC_M_READY;
+
+        /*
+         * The preceding store of msg->flags must occur before the following
+         * load of ch->local_GP->put.
+         */
+        mb();
+
+        /* see if the message is next in line to be sent, if so send it */
+
+        put = ch->local_GP->put;
+        if (put == msg_number) {
+                xpc_send_msgs(ch, put);
+        }
+
+        /* drop the reference grabbed in xpc_allocate_msg() */
+        xpc_msgqueue_deref(ch);
+        return ret;
+}
+
+
+/*
+ * Send a message previously allocated using xpc_initiate_allocate() on the
+ * specified channel connected to the specified partition.
+ *
+ * This routine will not wait for the message to be received, nor will
+ * notification be given when it does happen. Once this routine has returned
+ * the message entry allocated via xpc_initiate_allocate() is no longer
+ * accessable to the caller.
+ *
+ * This routine, although called by users, does not call xpc_part_ref() to
+ * ensure that the partition infrastructure is in place. It relies on the
+ * fact that we called xpc_msgqueue_ref() in xpc_allocate_msg().
+ *
+ * Arguments:
+ *
+ *      partid - ID of partition to which the channel is connected.
+ *      ch_number - channel # to send message on.
+ *      payload - pointer to the payload area allocated via
+ *                      xpc_initiate_allocate().
+ */
+enum xpc_retval
+xpc_initiate_send(partid_t partid, int ch_number, void *payload)
+{
+        struct xpc_partition *part = &xpc_partitions[partid];
+        struct xpc_msg *msg = XPC_MSG_ADDRESS(payload);
+        enum xpc_retval ret;
+
+
+        dev_dbg(xpc_chan, "msg=0x%p, partid=%d, channel=%d\n", (void *) msg,
+                partid, ch_number);
+
+        DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
+        DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
+        DBUG_ON(msg == NULL);
+
+        ret = xpc_send_msg(&part->channels[ch_number], msg, 0, NULL, NULL);
+
+        return ret;
+}
+
+
+/*
+ * Send a message previously allocated using xpc_initiate_allocate on the
+ * specified channel connected to the specified partition.
+ *
+ * This routine will not wait for the message to be sent. Once this routine
+ * has returned the message entry allocated via xpc_initiate_allocate() is no
+ * longer accessable to the caller.
+ *
+ * Once the remote end of the channel has received the message, the function
+ * passed as an argument to xpc_initiate_send_notify() will be called. This
+ * allows the sender to free up or re-use any buffers referenced by the
+ * message, but does NOT mean the message has been processed at the remote
+ * end by a receiver.
+ *
+ * If this routine returns an error, the caller's function will NOT be called.
+ *
+ * This routine, although called by users, does not call xpc_part_ref() to
+ * ensure that the partition infrastructure is in place. It relies on the
+ * fact that we called xpc_msgqueue_ref() in xpc_allocate_msg().
+ *
+ * Arguments:
+ *
+ *      partid - ID of partition to which the channel is connected.
+ *      ch_number - channel # to send message on.
+ *      payload - pointer to the payload area allocated via
+ *                      xpc_initiate_allocate().
+ *      func - function to call with asynchronous notification of message
+ *                receipt. THIS FUNCTION MUST BE NON-BLOCKING.
+ *      key - user-defined key to be passed to the function when it's called.
+ */
+enum xpc_retval
+xpc_initiate_send_notify(partid_t partid, int ch_number, void *payload,
+                                xpc_notify_func func, void *key)
+{
+        struct xpc_partition *part = &xpc_partitions[partid];
+        struct xpc_msg *msg = XPC_MSG_ADDRESS(payload);
+        enum xpc_retval ret;
+
+
+        dev_dbg(xpc_chan, "msg=0x%p, partid=%d, channel=%d\n", (void *) msg,
+                partid, ch_number);
+
+        DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
+        DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
+        DBUG_ON(msg == NULL);
+        DBUG_ON(func == NULL);
+
+        ret = xpc_send_msg(&part->channels[ch_number], msg, XPC_N_CALL,
+                                                                func, key);
+        return ret;
+}
+
+
+static struct xpc_msg *
+xpc_pull_remote_msg(struct xpc_channel *ch, s64 get)
+{
+        struct xpc_partition *part = &xpc_partitions[ch->partid];
+        struct xpc_msg *remote_msg, *msg;
+        u32 msg_index, nmsgs;
+        u64 msg_offset;
+        enum xpc_retval ret;
+
+
+        if (mutex_lock_interruptible(&ch->msg_to_pull_mutex) != 0) {
+                /* we were interrupted by a signal */
+                return NULL;
+        }
+
+        while (get >= ch->next_msg_to_pull) {
+
+                /* pull as many messages as are ready and able to be pulled */
+
+                msg_index = ch->next_msg_to_pull % ch->remote_nentries;
+
+                DBUG_ON(ch->next_msg_to_pull >=
+                                        (volatile s64) ch->w_remote_GP.put);
+                nmsgs =  (volatile s64) ch->w_remote_GP.put -
+                                                ch->next_msg_to_pull;
+                if (msg_index + nmsgs > ch->remote_nentries) {
+                        /* ignore the ones that wrap the msg queue for now */
+                        nmsgs = ch->remote_nentries - msg_index;
+                }
+
+                msg_offset = msg_index * ch->msg_size;
+                msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue +
+                                                                msg_offset);
+                remote_msg = (struct xpc_msg *) (ch->remote_msgqueue_pa +
+                                                                msg_offset);
+
+                if ((ret = xpc_pull_remote_cachelines(part, msg, remote_msg,
+                                nmsgs * ch->msg_size)) != xpcSuccess) {
+
+                        dev_dbg(xpc_chan, "failed to pull %d msgs starting with"
+                                " msg %ld from partition %d, channel=%d, "
+                                "ret=%d\n", nmsgs, ch->next_msg_to_pull,
+                                ch->partid, ch->number, ret);
+
+                        XPC_DEACTIVATE_PARTITION(part, ret);
+
+                        mutex_unlock(&ch->msg_to_pull_mutex);
+                        return NULL;
+                }
+
+                mb();   /* >>> this may not be needed, we're not sure */
+
+                ch->next_msg_to_pull += nmsgs;
+        }
+
+        mutex_unlock(&ch->msg_to_pull_mutex);
+
+        /* return the message we were looking for */
+        msg_offset = (get % ch->remote_nentries) * ch->msg_size;
+        msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue + msg_offset);
+
+        return msg;
+}
+
+
+/*
+ * Get a message to be delivered.
+ */
+static struct xpc_msg *
+xpc_get_deliverable_msg(struct xpc_channel *ch)
+{
+        struct xpc_msg *msg = NULL;
+        s64 get;
+
+
+        do {
+                if ((volatile u32) ch->flags & XPC_C_DISCONNECTING) {
+                        break;
+                }
+
+                get = (volatile s64) ch->w_local_GP.get;
+                if (get == (volatile s64) ch->w_remote_GP.put) {
+                        break;
+                }
+
+                /* There are messages waiting to be pulled and delivered.
+                 * We need to try to secure one for ourselves. We'll do this
+                 * by trying to increment w_local_GP.get and hope that no one
+                 * else beats us to it. If they do, we'll we'll simply have
+                 * to try again for the next one.
+                 */
+
+                if (cmpxchg(&ch->w_local_GP.get, get, get + 1) == get) {
+                        /* we got the entry referenced by get */
+
+                        dev_dbg(xpc_chan, "w_local_GP.get changed to %ld, "
+                                "partid=%d, channel=%d\n", get + 1,
+                                ch->partid, ch->number);
+
+                        /* pull the message from the remote partition */
+
+                        msg = xpc_pull_remote_msg(ch, get);
+
+                        DBUG_ON(msg != NULL && msg->number != get);
+                        DBUG_ON(msg != NULL && (msg->flags & XPC_M_DONE));
+                        DBUG_ON(msg != NULL && !(msg->flags & XPC_M_READY));
+
+                        break;
+                }
+
+        } while (1);
+
+        return msg;
+}
+
+
+/*
+ * Deliver a message to its intended recipient.
+ */
+void
+xpc_deliver_msg(struct xpc_channel *ch)
+{
+        struct xpc_msg *msg;
+
+
+        if ((msg = xpc_get_deliverable_msg(ch)) != NULL) {
+
+                /*
+                 * This ref is taken to protect the payload itself from being
+                 * freed before the user is finished with it, which the user
+                 * indicates by calling xpc_initiate_received().
+                 */
+                xpc_msgqueue_ref(ch);
+
+                atomic_inc(&ch->kthreads_active);
+
+                if (ch->func != NULL) {
+                        dev_dbg(xpc_chan, "ch->func() called, msg=0x%p, "
+                                "msg_number=%ld, partid=%d, channel=%d\n",
+                                (void *) msg, msg->number, ch->partid,
+                                ch->number);
+
+                        /* deliver the message to its intended recipient */
+                        ch->func(xpcMsgReceived, ch->partid, ch->number,
+                                        &msg->payload, ch->key);
+
+                        dev_dbg(xpc_chan, "ch->func() returned, msg=0x%p, "
+                                "msg_number=%ld, partid=%d, channel=%d\n",
+                                (void *) msg, msg->number, ch->partid,
+                                ch->number);
+                }
+
+                atomic_dec(&ch->kthreads_active);
+        }
+}
+
+
+/*
+ * Now we actually acknowledge the messages that have been delivered and ack'd
+ * by advancing the cached remote message queue's Get value and if requested
+ * send an IPI to the message sender's partition.
+ */
+static void
+xpc_acknowledge_msgs(struct xpc_channel *ch, s64 initial_get, u8 msg_flags)
+{
+        struct xpc_msg *msg;
+        s64 get = initial_get + 1;
+        int send_IPI = 0;
+
+
+        while (1) {
+
+                while (1) {
+                        if (get == (volatile s64) ch->w_local_GP.get) {
+                                break;
+                        }
+
+                        msg = (struct xpc_msg *) ((u64) ch->remote_msgqueue +
+                               (get % ch->remote_nentries) * ch->msg_size);
+
+                        if (!(msg->flags & XPC_M_DONE)) {
+                                break;
+                        }
+
+                        msg_flags |= msg->flags;
+                        get++;
+                }
+
+                if (get == initial_get) {
+                        /* nothing's changed */
+                        break;
+                }
+
+                if (cmpxchg_rel(&ch->local_GP->get, initial_get, get) !=
+                                                                initial_get) {
+                        /* someone else beat us to it */
+                        DBUG_ON((volatile s64) ch->local_GP->get <=
+                                                                initial_get);
+                        break;
+                }
+
+                /* we just set the new value of local_GP->get */
+
+                dev_dbg(xpc_chan, "local_GP->get changed to %ld, partid=%d, "
+                        "channel=%d\n", get, ch->partid, ch->number);
+
+                send_IPI = (msg_flags & XPC_M_INTERRUPT);
+
+                /*
+                 * We need to ensure that the message referenced by
+                 * local_GP->get is not XPC_M_DONE or that local_GP->get
+                 * equals w_local_GP.get, so we'll go have a look.
+                 */
+                initial_get = get;
+        }
+
+        if (send_IPI) {
+                xpc_IPI_send_msgrequest(ch);
+        }
+}
+
+
+/*
+ * Acknowledge receipt of a delivered message.
+ *
+ * If a message has XPC_M_INTERRUPT set, send an interrupt to the partition
+ * that sent the message.
+ *
+ * This function, although called by users, does not call xpc_part_ref() to
+ * ensure that the partition infrastructure is in place. It relies on the
+ * fact that we called xpc_msgqueue_ref() in xpc_deliver_msg().
+ *
+ * Arguments:
+ *
+ *      partid - ID of partition to which the channel is connected.
+ *      ch_number - channel # message received on.
+ *      payload - pointer to the payload area allocated via
+ *                      xpc_initiate_allocate().
+ */
+void
+xpc_initiate_received(partid_t partid, int ch_number, void *payload)
+{
+        struct xpc_partition *part = &xpc_partitions[partid];
+        struct xpc_channel *ch;
+        struct xpc_msg *msg = XPC_MSG_ADDRESS(payload);
+        s64 get, msg_number = msg->number;
+
+
+        DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);
+        DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
+
+        ch = &part->channels[ch_number];
+
+        dev_dbg(xpc_chan, "msg=0x%p, msg_number=%ld, partid=%d, channel=%d\n",
+                (void *) msg, msg_number, ch->partid, ch->number);
+
+        DBUG_ON((((u64) msg - (u64) ch->remote_msgqueue) / ch->msg_size) !=
+                                        msg_number % ch->remote_nentries);
+        DBUG_ON(msg->flags & XPC_M_DONE);
+
+        msg->flags |= XPC_M_DONE;
+
+        /*
+         * The preceding store of msg->flags must occur before the following
+         * load of ch->local_GP->get.
+         */
+        mb();
+
+        /*
+         * See if this message is next in line to be acknowledged as having
+         * been delivered.
+         */
+        get = ch->local_GP->get;
+        if (get == msg_number) {
+                xpc_acknowledge_msgs(ch, get, msg->flags);
+        }
+
+        /* the call to xpc_msgqueue_ref() was done by xpc_deliver_msg()  */
+        xpc_msgqueue_deref(ch);
+}
+