dmaengine: introduce dma_request_channel and private channels

This interface is primarily for device-to-memory clients which need to
search for dma channels with platform-specific characteristics.  The
prototype is:

struct dma_chan *dma_request_channel(dma_cap_mask_t mask,
                                     dma_filter_fn filter_fn,
                                     void *filter_param);

When the optional 'filter_fn' parameter is set to NULL
dma_request_channel simply returns the first channel that satisfies the
capability mask.  Otherwise, when the mask parameter is insufficient for
specifying the necessary channel, the filter_fn routine can be used to
disposition the available channels in the system. The filter_fn routine
is called once for each free channel in the system.  Upon seeing a
suitable channel filter_fn returns DMA_ACK which flags that channel to
be the return value from dma_request_channel.  A channel allocated via
this interface is exclusive to the caller, until dma_release_channel()
is called.

To ensure that all channels are not consumed by the general-purpose
allocator the DMA_PRIVATE capability is provided to exclude a dma_device
from general-purpose (memory-to-memory) consideration.

Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

2 files changed, 155 insertions, 16 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 418eca28d472..7a0594f24a3f 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -134,14 +134,14 @@ static struct class dma_devclass = {
 
 /* --- client and device registration --- */
 
-#define dma_chan_satisfies_mask(chan, mask) \
-        __dma_chan_satisfies_mask((chan), &(mask))
+#define dma_device_satisfies_mask(device, mask) \
+        __dma_device_satisfies_mask((device), &(mask))
 static int
-__dma_chan_satisfies_mask(struct dma_chan *chan, dma_cap_mask_t *want)
+__dma_device_satisfies_mask(struct dma_device *device, dma_cap_mask_t *want)
 {
         dma_cap_mask_t has;
 
-        bitmap_and(has.bits, want->bits, chan->device->cap_mask.bits,
+        bitmap_and(has.bits, want->bits, device->cap_mask.bits,
                 DMA_TX_TYPE_END);
         return bitmap_equal(want->bits, has.bits, DMA_TX_TYPE_END);
 }
@@ -195,7 +195,7 @@ static int dma_chan_get(struct dma_chan *chan)
                         err = desc_cnt;
                         chan->client_count = 0;
                         module_put(owner);
-                } else
+                } else if (!dma_has_cap(DMA_PRIVATE, chan->device->cap_mask))
                         balance_ref_count(chan);
         }
 
@@ -232,14 +232,16 @@ static void dma_client_chan_alloc(struct dma_client *client)
 
         /* Find a channel */
         list_for_each_entry(device, &dma_device_list, global_node) {
+                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
+                        continue;
                 /* Does the client require a specific DMA controller? */
                 if (client->slave && client->slave->dma_dev
                                 && client->slave->dma_dev != device->dev)
                         continue;
+                if (!dma_device_satisfies_mask(device, client->cap_mask))
+                        continue;
 
                 list_for_each_entry(chan, &device->channels, device_node) {
-                        if (!dma_chan_satisfies_mask(chan, client->cap_mask))
-                                continue;
                         if (!chan->client_count)
                                 continue;
                         ack = client->event_callback(client, chan,
@@ -320,11 +322,12 @@ static int __init dma_channel_table_init(void)
 
         bitmap_fill(dma_cap_mask_all.bits, DMA_TX_TYPE_END);
 
-        /* 'interrupt' and 'slave' are channel capabilities, but are not
-         * associated with an operation so they do not need an entry in the
-         * channel_table
+        /* 'interrupt', 'private', and 'slave' are channel capabilities,
+         * but are not associated with an operation so they do not need
+         * an entry in the channel_table
          */
         clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);
+        clear_bit(DMA_PRIVATE, dma_cap_mask_all.bits);
         clear_bit(DMA_SLAVE, dma_cap_mask_all.bits);
 
         for_each_dma_cap_mask(cap, dma_cap_mask_all) {
@@ -378,10 +381,13 @@ void dma_issue_pending_all(void)
                   "client called %s without a reference", __func__);
 
         rcu_read_lock();
-        list_for_each_entry_rcu(device, &dma_device_list, global_node)
+        list_for_each_entry_rcu(device, &dma_device_list, global_node) {
+                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
+                        continue;
                 list_for_each_entry(chan, &device->channels, device_node)
                         if (chan->client_count)
                                 device->device_issue_pending(chan);
+        }
         rcu_read_unlock();
 }
 EXPORT_SYMBOL(dma_issue_pending_all);
@@ -403,7 +409,8 @@ static struct dma_chan *nth_chan(enum dma_transaction_type cap, int n)
         struct dma_chan *min = NULL;
 
         list_for_each_entry(device, &dma_device_list, global_node) {
-                if (!dma_has_cap(cap, device->cap_mask))
+                if (!dma_has_cap(cap, device->cap_mask) ||
+                    dma_has_cap(DMA_PRIVATE, device->cap_mask))
                         continue;
                 list_for_each_entry(chan, &device->channels, device_node) {
                         if (!chan->client_count)
@@ -452,9 +459,12 @@ static void dma_channel_rebalance(void)
                 for_each_possible_cpu(cpu)
                         per_cpu_ptr(channel_table[cap], cpu)->chan = NULL;
 
-        list_for_each_entry(device, &dma_device_list, global_node)
+        list_for_each_entry(device, &dma_device_list, global_node) {
+                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
+                        continue;
                 list_for_each_entry(chan, &device->channels, device_node)
                         chan->table_count = 0;
+        }
 
         /* don't populate the channel_table if no clients are available */
         if (!dmaengine_ref_count)
@@ -473,6 +483,111 @@ static void dma_channel_rebalance(void)
                 }
 }
 
+static struct dma_chan *private_candidate(dma_cap_mask_t *mask, struct dma_device *dev)
+{
+        struct dma_chan *chan;
+        struct dma_chan *ret = NULL;
+
+        if (!__dma_device_satisfies_mask(dev, mask)) {
+                pr_debug("%s: wrong capabilities\n", __func__);
+                return NULL;
+        }
+        /* devices with multiple channels need special handling as we need to
+         * ensure that all channels are either private or public.
+         */
+        if (dev->chancnt > 1 && !dma_has_cap(DMA_PRIVATE, dev->cap_mask))
+                list_for_each_entry(chan, &dev->channels, device_node) {
+                        /* some channels are already publicly allocated */
+                        if (chan->client_count)
+                                return NULL;
+                }
+
+        list_for_each_entry(chan, &dev->channels, device_node) {
+                if (chan->client_count) {
+                        pr_debug("%s: %s busy\n",
+                                 __func__, dev_name(&chan->dev));
+                        continue;
+                }
+                ret = chan;
+                break;
+        }
+
+        return ret;
+}
+
+/**
+ * dma_request_channel - try to allocate an exclusive channel
+ * @mask: capabilities that the channel must satisfy
+ * @fn: optional callback to disposition available channels
+ * @fn_param: opaque parameter to pass to dma_filter_fn
+ */
+struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, void *fn_param)
+{
+        struct dma_device *device, *_d;
+        struct dma_chan *chan = NULL;
+        enum dma_state_client ack;
+        int err;
+
+        /* Find a channel */
+        mutex_lock(&dma_list_mutex);
+        list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
+                chan = private_candidate(mask, device);
+                if (!chan)
+                        continue;
+
+                if (fn)
+                        ack = fn(chan, fn_param);
+                else
+                        ack = DMA_ACK;
+
+                if (ack == DMA_ACK) {
+                        /* Found a suitable channel, try to grab, prep, and
+                         * return it.  We first set DMA_PRIVATE to disable
+                         * balance_ref_count as this channel will not be
+                         * published in the general-purpose allocator
+                         */
+                        dma_cap_set(DMA_PRIVATE, device->cap_mask);
+                        err = dma_chan_get(chan);
+
+                        if (err == -ENODEV) {
+                                pr_debug("%s: %s module removed\n", __func__,
+                                         dev_name(&chan->dev));
+                                list_del_rcu(&device->global_node);
+                        } else if (err)
+                                pr_err("dmaengine: failed to get %s: (%d)\n",
+                                       dev_name(&chan->dev), err);
+                        else
+                                break;
+                } else if (ack == DMA_DUP) {
+                        pr_debug("%s: %s filter said DMA_DUP\n",
+                                 __func__, dev_name(&chan->dev));
+                } else if (ack == DMA_NAK) {
+                        pr_debug("%s: %s filter said DMA_NAK\n",
+                                 __func__, dev_name(&chan->dev));
+                        break;
+                } else
+                        WARN_ONCE(1, "filter_fn: unknown response?\n");
+                chan = NULL;
+        }
+        mutex_unlock(&dma_list_mutex);
+
+        pr_debug("%s: %s (%s)\n", __func__, chan ? "success" : "fail",
+                 chan ? dev_name(&chan->dev) : NULL);
+
+        return chan;
+}
+EXPORT_SYMBOL_GPL(__dma_request_channel);
+
+void dma_release_channel(struct dma_chan *chan)
+{
+        mutex_lock(&dma_list_mutex);
+        WARN_ONCE(chan->client_count != 1,
+                  "chan reference count %d != 1\n", chan->client_count);
+        dma_chan_put(chan);
+        mutex_unlock(&dma_list_mutex);
+}
+EXPORT_SYMBOL_GPL(dma_release_channel);
+
 /**
  * dma_chans_notify_available - broadcast available channels to the clients
  */
@@ -506,7 +621,9 @@ void dma_async_client_register(struct dma_client *client)
         dmaengine_ref_count++;
 
         /* try to grab channels */
-        list_for_each_entry_safe(device, _d, &dma_device_list, global_node)
+        list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
+                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
+                        continue;
                 list_for_each_entry(chan, &device->channels, device_node) {
                         err = dma_chan_get(chan);
                         if (err == -ENODEV) {
@@ -517,6 +634,7 @@ void dma_async_client_register(struct dma_client *client)
                                 pr_err("dmaengine: failed to get %s: (%d)\n",
                                        dev_name(&chan->dev), err);
                 }
+        }
 
         /* if this is the first reference and there were channels
          * waiting we need to rebalance to get those channels
@@ -547,9 +665,12 @@ void dma_async_client_unregister(struct dma_client *client)
         dmaengine_ref_count--;
         BUG_ON(dmaengine_ref_count < 0);
         /* drop channel references */
-        list_for_each_entry(device, &dma_device_list, global_node)
+        list_for_each_entry(device, &dma_device_list, global_node) {
+                if (dma_has_cap(DMA_PRIVATE, device->cap_mask))
+                        continue;
                 list_for_each_entry(chan, &device->channels, device_node)
                         dma_chan_put(chan);
+        }
 
         list_del(&client->global_node);
         mutex_unlock(&dma_list_mutex);
@@ -639,9 +760,11 @@ int dma_async_device_register(struct dma_device *device)
                 chan->slow_ref = 0;
                 INIT_RCU_HEAD(&chan->rcu);
         }
+        device->chancnt = chancnt;
 
         mutex_lock(&dma_list_mutex);
-        if (dmaengine_ref_count)
+        /* take references on public channels */
+        if (dmaengine_ref_count && !dma_has_cap(DMA_PRIVATE, device->cap_mask))
                 list_for_each_entry(chan, &device->channels, device_node) {
                         /* if clients are already waiting for channels we need
                          * to take references on their behalf
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 57a43adfc39e..fe40bc020af6 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -89,6 +89,7 @@ enum dma_transaction_type {
         DMA_MEMSET,
         DMA_MEMCPY_CRC32C,
         DMA_INTERRUPT,
+        DMA_PRIVATE,
         DMA_SLAVE,
 };
 
@@ -224,6 +225,18 @@ typedef enum dma_state_client (*dma_event_callback) (struct dma_client *client,
                 struct dma_chan *chan, enum dma_state state);
 
 /**
+ * typedef dma_filter_fn - callback filter for dma_request_channel
+ * @chan: channel to be reviewed
+ * @filter_param: opaque parameter passed through dma_request_channel
+ *
+ * When this optional parameter is specified in a call to dma_request_channel a
+ * suitable channel is passed to this routine for further dispositioning before
+ * being returned.  Where 'suitable' indicates a non-busy channel that
+ * satisfies the given capability mask.
+ */
+typedef enum dma_state_client (*dma_filter_fn)(struct dma_chan *chan, void *filter_param);
+
+/**
  * struct dma_client - info on the entity making use of DMA services
  * @event_callback: func ptr to call when something happens
  * @cap_mask: only return channels that satisfy the requested capabilities
@@ -472,6 +485,9 @@ void dma_async_device_unregister(struct dma_device *device);
 void dma_run_dependencies(struct dma_async_tx_descriptor *tx);
 struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type);
 void dma_issue_pending_all(void);
+#define dma_request_channel(mask, x, y) __dma_request_channel(&(mask), x, y)
+struct dma_chan *__dma_request_channel(dma_cap_mask_t *mask, dma_filter_fn fn, void *fn_param);
+void dma_release_channel(struct dma_chan *chan);
 
 /* --- Helper iov-locking functions --- */