USB: xhci: No-op command queueing and irq handler.

xHCI host controllers can optionally implement a no-op test.  This
simple test ensures the OS has correctly setup all basic data structures
and can correctly respond to interrupts from the host controller
hardware.

There are two rings exercised by the no-op test:  the command ring, and
the event ring.

The host controller driver writes a no-op command TRB to the command
ring, and rings the doorbell for the command ring (the first entry in
the doorbell array).  The hardware receives this event, places a command
completion event on the event ring, and fires an interrupt.

The host controller driver sees the interrupt, and checks the event ring
for TRBs it can process, and sees the command completion event.  (See
the rules in xhci-ring.c for who "owns" a TRB.  This is a simplified set
of rules, and may not contain all the details that are in the xHCI 0.95
spec.)

A timer fires every 60 seconds to debug the state of the hardware and
command and event rings.  This timer only runs if
CONFIG_USB_XHCI_HCD_DEBUGGING is 'y'.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

6 files changed, 647 insertions, 13 deletions

diff --git a/drivers/usb/host/xhci-dbg.c b/drivers/usb/host/xhci-dbg.c
index 5724683cef16..6dbf7d856f80 100644
--- a/drivers/usb/host/xhci-dbg.c
+++ b/drivers/usb/host/xhci-dbg.c
@@ -230,6 +230,64 @@ void xhci_print_registers(struct xhci_hcd *xhci)
         xhci_print_op_regs(xhci);
 }
 
+void xhci_print_trb_offsets(struct xhci_hcd *xhci, union xhci_trb *trb)
+{
+        int i;
+        for (i = 0; i < 4; ++i)
+                xhci_dbg(xhci, "Offset 0x%x = 0x%x\n",
+                                i*4, trb->generic.field[i]);
+}
+
+/**
+ * Debug a transfer request block (TRB).
+ */
+void xhci_debug_trb(struct xhci_hcd *xhci, union xhci_trb *trb)
+{
+        u64     address;
+        u32     type = xhci_readl(xhci, &trb->link.control) & TRB_TYPE_BITMASK;
+
+        switch (type) {
+        case TRB_TYPE(TRB_LINK):
+                xhci_dbg(xhci, "Link TRB:\n");
+                xhci_print_trb_offsets(xhci, trb);
+
+                address = trb->link.segment_ptr[0] +
+                        (((u64) trb->link.segment_ptr[1]) << 32);
+                xhci_dbg(xhci, "Next ring segment DMA address = 0x%llx\n", address);
+
+                xhci_dbg(xhci, "Interrupter target = 0x%x\n",
+                                GET_INTR_TARGET(trb->link.intr_target));
+                xhci_dbg(xhci, "Cycle bit = %u\n",
+                                (unsigned int) (trb->link.control & TRB_CYCLE));
+                xhci_dbg(xhci, "Toggle cycle bit = %u\n",
+                                (unsigned int) (trb->link.control & LINK_TOGGLE));
+                xhci_dbg(xhci, "No Snoop bit = %u\n",
+                                (unsigned int) (trb->link.control & TRB_NO_SNOOP));
+                break;
+        case TRB_TYPE(TRB_TRANSFER):
+                address = trb->trans_event.buffer[0] +
+                        (((u64) trb->trans_event.buffer[1]) << 32);
+                /*
+                 * FIXME: look at flags to figure out if it's an address or if
+                 * the data is directly in the buffer field.
+                 */
+                xhci_dbg(xhci, "DMA address or buffer contents= %llu\n", address);
+                break;
+        case TRB_TYPE(TRB_COMPLETION):
+                address = trb->event_cmd.cmd_trb[0] +
+                        (((u64) trb->event_cmd.cmd_trb[1]) << 32);
+                xhci_dbg(xhci, "Command TRB pointer = %llu\n", address);
+                xhci_dbg(xhci, "Completion status = %u\n",
+                                (unsigned int) GET_COMP_CODE(trb->event_cmd.status));
+                xhci_dbg(xhci, "Flags = 0x%x\n", (unsigned int) trb->event_cmd.flags);
+                break;
+        default:
+                xhci_dbg(xhci, "Unknown TRB with TRB type ID %u\n",
+                                (unsigned int) type>>10);
+                xhci_print_trb_offsets(xhci, trb);
+                break;
+        }
+}
 
 /**
  * Debug a segment with an xHCI ring.
@@ -261,6 +319,20 @@ void xhci_debug_segment(struct xhci_hcd *xhci, struct xhci_segment *seg)
         }
 }
 
+void xhci_dbg_ring_ptrs(struct xhci_hcd *xhci, struct xhci_ring *ring)
+{
+        xhci_dbg(xhci, "Ring deq = 0x%x (virt), 0x%x (dma)\n",
+                        (unsigned int) ring->dequeue,
+                        trb_virt_to_dma(ring->deq_seg, ring->dequeue));
+        xhci_dbg(xhci, "Ring deq updated %u times\n",
+                        ring->deq_updates);
+        xhci_dbg(xhci, "Ring enq = 0x%x (virt), 0x%x (dma)\n",
+                        (unsigned int) ring->enqueue,
+                        trb_virt_to_dma(ring->enq_seg, ring->enqueue));
+        xhci_dbg(xhci, "Ring enq updated %u times\n",
+                        ring->enq_updates);
+}
+
 /**
  * Debugging for an xHCI ring, which is a queue broken into multiple segments.
  *
@@ -277,6 +349,10 @@ void xhci_debug_ring(struct xhci_hcd *xhci, struct xhci_ring *ring)
         struct xhci_segment *first_seg = ring->first_seg;
         xhci_debug_segment(xhci, first_seg);
 
+        if (!ring->enq_updates && !ring->deq_updates) {
+                xhci_dbg(xhci, "  Ring has not been updated\n");
+                return;
+        }
         for (seg = first_seg->next; seg != first_seg; seg = seg->next)
                 xhci_debug_segment(xhci, seg);
 }
diff --git a/drivers/usb/host/xhci-hcd.c b/drivers/usb/host/xhci-hcd.c
index 011f47810665..a99c119e9fd9 100644
--- a/drivers/usb/host/xhci-hcd.c
+++ b/drivers/usb/host/xhci-hcd.c
@@ -218,6 +218,120 @@ int xhci_init(struct usb_hcd *hcd)
 }
 
 /*
+ * Called in interrupt context when there might be work
+ * queued on the event ring
+ *
+ * xhci->lock must be held by caller.
+ */
+static void xhci_work(struct xhci_hcd *xhci)
+{
+        u32 temp;
+
+        /*
+         * Clear the op reg interrupt status first,
+         * so we can receive interrupts from other MSI-X interrupters.
+         * Write 1 to clear the interrupt status.
+         */
+        temp = xhci_readl(xhci, &xhci->op_regs->status);
+        temp |= STS_EINT;
+        xhci_writel(xhci, temp, &xhci->op_regs->status);
+        /* FIXME when MSI-X is supported and there are multiple vectors */
+        /* Clear the MSI-X event interrupt status */
+
+        /* Acknowledge the interrupt */
+        temp = xhci_readl(xhci, &xhci->ir_set->irq_pending);
+        temp |= 0x3;
+        xhci_writel(xhci, temp, &xhci->ir_set->irq_pending);
+        /* Flush posted writes */
+        xhci_readl(xhci, &xhci->ir_set->irq_pending);
+
+        /* FIXME this should be a delayed service routine that clears the EHB */
+        handle_event(xhci);
+
+        /* Clear the event handler busy flag; the event ring should be empty. */
+        temp = xhci_readl(xhci, &xhci->ir_set->erst_dequeue[0]);
+        xhci_writel(xhci, temp & ~ERST_EHB, &xhci->ir_set->erst_dequeue[0]);
+        /* Flush posted writes -- FIXME is this necessary? */
+        xhci_readl(xhci, &xhci->ir_set->irq_pending);
+}
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * xHCI spec says we can get an interrupt, and if the HC has an error condition,
+ * we might get bad data out of the event ring.  Section 4.10.2.7 has a list of
+ * indicators of an event TRB error, but we check the status *first* to be safe.
+ */
+irqreturn_t xhci_irq(struct usb_hcd *hcd)
+{
+        struct xhci_hcd *xhci = hcd_to_xhci(hcd);
+        u32 temp, temp2;
+
+        spin_lock(&xhci->lock);
+        /* Check if the xHC generated the interrupt, or the irq is shared */
+        temp = xhci_readl(xhci, &xhci->op_regs->status);
+        temp2 = xhci_readl(xhci, &xhci->ir_set->irq_pending);
+        if (!(temp & STS_EINT) && !ER_IRQ_PENDING(temp2)) {
+                spin_unlock(&xhci->lock);
+                return IRQ_NONE;
+        }
+
+        temp = xhci_readl(xhci, &xhci->op_regs->status);
+        if (temp & STS_FATAL) {
+                xhci_warn(xhci, "WARNING: Host System Error\n");
+                xhci_halt(xhci);
+                xhci_to_hcd(xhci)->state = HC_STATE_HALT;
+                return -ESHUTDOWN;
+        }
+
+        xhci_work(xhci);
+        spin_unlock(&xhci->lock);
+
+        return IRQ_HANDLED;
+}
+
+#ifdef CONFIG_USB_XHCI_HCD_DEBUGGING
+void event_ring_work(unsigned long arg)
+{
+        unsigned long flags;
+        int temp;
+        struct xhci_hcd *xhci = (struct xhci_hcd *) arg;
+        int i, j;
+
+        xhci_dbg(xhci, "Poll event ring: %lu\n", jiffies);
+
+        spin_lock_irqsave(&xhci->lock, flags);
+        temp = xhci_readl(xhci, &xhci->op_regs->status);
+        xhci_dbg(xhci, "op reg status = 0x%x\n", temp);
+        temp = xhci_readl(xhci, &xhci->ir_set->irq_pending);
+        xhci_dbg(xhci, "ir_set 0 pending = 0x%x\n", temp);
+        xhci_dbg(xhci, "No-op commands handled = %d\n", xhci->noops_handled);
+        xhci_dbg(xhci, "HC error bitmask = 0x%x\n", xhci->error_bitmask);
+        xhci->error_bitmask = 0;
+        xhci_dbg(xhci, "Event ring:\n");
+        xhci_debug_segment(xhci, xhci->event_ring->deq_seg);
+        xhci_dbg_ring_ptrs(xhci, xhci->event_ring);
+        temp = xhci_readl(xhci, &xhci->ir_set->erst_dequeue[0]);
+        temp &= ERST_PTR_MASK;
+        xhci_dbg(xhci, "ERST deq = 0x%x\n", temp);
+        xhci_dbg(xhci, "Command ring:\n");
+        xhci_debug_segment(xhci, xhci->cmd_ring->deq_seg);
+        xhci_dbg_ring_ptrs(xhci, xhci->cmd_ring);
+        xhci_dbg_cmd_ptrs(xhci);
+
+        if (xhci->noops_submitted != NUM_TEST_NOOPS)
+                if (setup_one_noop(xhci))
+                        ring_cmd_db(xhci);
+        spin_unlock_irqrestore(&xhci->lock, flags);
+
+        if (!xhci->zombie)
+                mod_timer(&xhci->event_ring_timer, jiffies + POLL_TIMEOUT * HZ);
+        else
+                xhci_dbg(xhci, "Quit polling the event ring.\n");
+}
+#endif
+
+/*
  * Start the HC after it was halted.
  *
  * This function is called by the USB core when the HC driver is added.
@@ -233,8 +347,9 @@ int xhci_run(struct usb_hcd *hcd)
 {
         u32 temp;
         struct xhci_hcd *xhci = hcd_to_xhci(hcd);
-        xhci_dbg(xhci, "xhci_run\n");
+        void (*doorbell)(struct xhci_hcd *) = NULL;
 
+        xhci_dbg(xhci, "xhci_run\n");
 #if 0   /* FIXME: MSI not setup yet */
         /* Do this at the very last minute */
         ret = xhci_setup_msix(xhci);
@@ -243,6 +358,17 @@ int xhci_run(struct usb_hcd *hcd)
 
         return -ENOSYS;
 #endif
+#ifdef CONFIG_USB_XHCI_HCD_DEBUGGING
+        init_timer(&xhci->event_ring_timer);
+        xhci->event_ring_timer.data = (unsigned long) xhci;
+        xhci->event_ring_timer.function = event_ring_work;
+        /* Poll the event ring */
+        xhci->event_ring_timer.expires = jiffies + POLL_TIMEOUT * HZ;
+        xhci->zombie = 0;
+        xhci_dbg(xhci, "Setting event ring polling timer\n");
+        add_timer(&xhci->event_ring_timer);
+#endif
+
         xhci_dbg(xhci, "// Set the interrupt modulation register\n");
         temp = xhci_readl(xhci, &xhci->ir_set->irq_control);
         temp &= 0xffff;
@@ -266,10 +392,24 @@ int xhci_run(struct usb_hcd *hcd)
                         &xhci->ir_set->irq_pending);
         xhci_print_ir_set(xhci, xhci->ir_set, 0);
 
+        if (NUM_TEST_NOOPS > 0)
+                doorbell = setup_one_noop(xhci);
+
         xhci_dbg(xhci, "Command ring memory map follows:\n");
         xhci_debug_ring(xhci, xhci->cmd_ring);
+        xhci_dbg_ring_ptrs(xhci, xhci->cmd_ring);
+        xhci_dbg_cmd_ptrs(xhci);
+
         xhci_dbg(xhci, "ERST memory map follows:\n");
         xhci_dbg_erst(xhci, &xhci->erst);
+        xhci_dbg(xhci, "Event ring:\n");
+        xhci_debug_ring(xhci, xhci->event_ring);
+        xhci_dbg_ring_ptrs(xhci, xhci->event_ring);
+        temp = xhci_readl(xhci, &xhci->ir_set->erst_dequeue[1]);
+        xhci_dbg(xhci, "ERST deq upper = 0x%x\n", temp);
+        temp = xhci_readl(xhci, &xhci->ir_set->erst_dequeue[0]);
+        temp &= ERST_PTR_MASK;
+        xhci_dbg(xhci, "ERST deq = 0x%x\n", temp);
 
         temp = xhci_readl(xhci, &xhci->op_regs->command);
         temp |= (CMD_RUN);
@@ -280,6 +420,8 @@ int xhci_run(struct usb_hcd *hcd)
         temp = xhci_readl(xhci, &xhci->op_regs->command);
         xhci_dbg(xhci, "// @%x = 0x%x\n",
                         (unsigned int) &xhci->op_regs->command, temp);
+        if (doorbell)
+                (*doorbell)(xhci);
 
         xhci_dbg(xhci, "Finished xhci_run\n");
         return 0;
@@ -309,6 +451,12 @@ void xhci_stop(struct usb_hcd *hcd)
 #if 0   /* No MSI yet */
         xhci_cleanup_msix(xhci);
 #endif
+#ifdef CONFIG_USB_XHCI_HCD_DEBUGGING
+        /* Tell the event ring poll function not to reschedule */
+        xhci->zombie = 1;
+        del_timer_sync(&xhci->event_ring_timer);
+#endif
+
         xhci_dbg(xhci, "// Disabling event ring interrupts\n");
         temp = xhci_readl(xhci, &xhci->op_regs->status);
         xhci_writel(xhci, temp & ~STS_EINT, &xhci->op_regs->status);
@@ -346,6 +494,8 @@ void xhci_shutdown(struct usb_hcd *hcd)
                     xhci_readl(xhci, &xhci->op_regs->status));
 }
 
+/*-------------------------------------------------------------------------*/
+
 int xhci_get_frame(struct usb_hcd *hcd)
 {
         struct xhci_hcd *xhci = hcd_to_xhci(hcd);
diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index be5a05b2021c..005d44641d81 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -172,7 +172,9 @@ static struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci,
         }
         /* The ring is empty, so the enqueue pointer == dequeue pointer */
         ring->enqueue = ring->first_seg->trbs;
+        ring->enq_seg = ring->first_seg;
         ring->dequeue = ring->enqueue;
+        ring->deq_seg = ring->first_seg;
         /* The ring is initialized to 0. The producer must write 1 to the cycle
          * bit to handover ownership of the TRB, so PCS = 1.  The consumer must
          * compare CCS to the cycle bit to check ownership, so CCS = 1.
@@ -374,14 +376,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
         xhci_writel(xhci, val, &xhci->ir_set->erst_base[0]);
 
         /* Set the event ring dequeue address */
-        xhci_dbg(xhci, "// Set ERST dequeue address for ir_set 0 = 0x%x%x\n",
-                        xhci->erst.entries[0].seg_addr[1], xhci->erst.entries[0].seg_addr[0]);
-        val = xhci_readl(xhci, &xhci->run_regs->ir_set[0].erst_dequeue[0]);
-        val &= ERST_PTR_MASK;
-        val |= (xhci->erst.entries[0].seg_addr[0] & ~ERST_PTR_MASK);
-        xhci_writel(xhci, val, &xhci->run_regs->ir_set[0].erst_dequeue[0]);
-        xhci_writel(xhci, xhci->erst.entries[0].seg_addr[1],
-                        &xhci->run_regs->ir_set[0].erst_dequeue[1]);
+        set_hc_event_deq(xhci);
         xhci_dbg(xhci, "Wrote ERST address to ir_set 0.\n");
         xhci_print_ir_set(xhci, xhci->ir_set, 0);
 
diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
index 4015082adf60..89614af80d20 100644
--- a/drivers/usb/host/xhci-pci.c
+++ b/drivers/usb/host/xhci-pci.c
@@ -96,6 +96,7 @@ static const struct hc_driver xhci_pci_hc_driver = {
         /*
          * generic hardware linkage
          */
+        .irq =                  xhci_irq,
         .flags =                HCD_MEMORY | HCD_USB3,
 
         /*
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
new file mode 100644
index 000000000000..c7e3c7142b9d
--- /dev/null
+++ b/drivers/usb/host/xhci-ring.c
@@ -0,0 +1,367 @@
+/*
+ * xHCI host controller driver
+ *
+ * Copyright (C) 2008 Intel Corp.
+ *
+ * Author: Sarah Sharp
+ * Some code borrowed from the Linux EHCI driver.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+/*
+ * Ring initialization rules:
+ * 1. Each segment is initialized to zero, except for link TRBs.
+ * 2. Ring cycle state = 0.  This represents Producer Cycle State (PCS) or
+ *    Consumer Cycle State (CCS), depending on ring function.
+ * 3. Enqueue pointer = dequeue pointer = address of first TRB in the segment.
+ *
+ * Ring behavior rules:
+ * 1. A ring is empty if enqueue == dequeue.  This means there will always be at
+ *    least one free TRB in the ring.  This is useful if you want to turn that
+ *    into a link TRB and expand the ring.
+ * 2. When incrementing an enqueue or dequeue pointer, if the next TRB is a
+ *    link TRB, then load the pointer with the address in the link TRB.  If the
+ *    link TRB had its toggle bit set, you may need to update the ring cycle
+ *    state (see cycle bit rules).  You may have to do this multiple times
+ *    until you reach a non-link TRB.
+ * 3. A ring is full if enqueue++ (for the definition of increment above)
+ *    equals the dequeue pointer.
+ *
+ * Cycle bit rules:
+ * 1. When a consumer increments a dequeue pointer and encounters a toggle bit
+ *    in a link TRB, it must toggle the ring cycle state.
+ * 2. When a producer increments an enqueue pointer and encounters a toggle bit
+ *    in a link TRB, it must toggle the ring cycle state.
+ *
+ * Producer rules:
+ * 1. Check if ring is full before you enqueue.
+ * 2. Write the ring cycle state to the cycle bit in the TRB you're enqueuing.
+ *    Update enqueue pointer between each write (which may update the ring
+ *    cycle state).
+ * 3. Notify consumer.  If SW is producer, it rings the doorbell for command
+ *    and endpoint rings.  If HC is the producer for the event ring,
+ *    and it generates an interrupt according to interrupt modulation rules.
+ *
+ * Consumer rules:
+ * 1. Check if TRB belongs to you.  If the cycle bit == your ring cycle state,
+ *    the TRB is owned by the consumer.
+ * 2. Update dequeue pointer (which may update the ring cycle state) and
+ *    continue processing TRBs until you reach a TRB which is not owned by you.
+ * 3. Notify the producer.  SW is the consumer for the event ring, and it
+ *   updates event ring dequeue pointer.  HC is the consumer for the command and
+ *   endpoint rings; it generates events on the event ring for these.
+ */
+
+#include "xhci.h"
+
+/*
+ * Returns zero if the TRB isn't in this segment, otherwise it returns the DMA
+ * address of the TRB.
+ */
+dma_addr_t trb_virt_to_dma(struct xhci_segment *seg,
+                union xhci_trb *trb)
+{
+        unsigned int offset;
+
+        if (!seg || !trb || (void *) trb < (void *) seg->trbs)
+                return 0;
+        /* offset in bytes, since these are byte-addressable */
+        offset = (unsigned int) trb - (unsigned int) seg->trbs;
+        /* SEGMENT_SIZE in bytes, trbs are 16-byte aligned */
+        if (offset > SEGMENT_SIZE || (offset % sizeof(*trb)) != 0)
+                return 0;
+        return seg->dma + offset;
+}
+
+/* Does this link TRB point to the first segment in a ring,
+ * or was the previous TRB the last TRB on the last segment in the ERST?
+ */
+static inline bool last_trb_on_last_seg(struct xhci_hcd *xhci, struct xhci_ring *ring,
+                struct xhci_segment *seg, union xhci_trb *trb)
+{
+        if (ring == xhci->event_ring)
+                return (trb == &seg->trbs[TRBS_PER_SEGMENT]) &&
+                        (seg->next == xhci->event_ring->first_seg);
+        else
+                return trb->link.control & LINK_TOGGLE;
+}
+
+/* Is this TRB a link TRB or was the last TRB the last TRB in this event ring
+ * segment?  I.e. would the updated event TRB pointer step off the end of the
+ * event seg?
+ */
+static inline int last_trb(struct xhci_hcd *xhci, struct xhci_ring *ring,
+                struct xhci_segment *seg, union xhci_trb *trb)
+{
+        if (ring == xhci->event_ring)
+                return trb == &seg->trbs[TRBS_PER_SEGMENT];
+        else
+                return (trb->link.control & TRB_TYPE_BITMASK) == TRB_TYPE(TRB_LINK);
+}
+
+/*
+ * See Cycle bit rules. SW is the consumer for the event ring only.
+ * Don't make a ring full of link TRBs.  That would be dumb and this would loop.
+ */
+static void inc_deq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer)
+{
+        union xhci_trb *next = ++(ring->dequeue);
+
+        ring->deq_updates++;
+        /* Update the dequeue pointer further if that was a link TRB or we're at
+         * the end of an event ring segment (which doesn't have link TRBS)
+         */
+        while (last_trb(xhci, ring, ring->deq_seg, next)) {
+                if (consumer && last_trb_on_last_seg(xhci, ring, ring->deq_seg, next)) {
+                        ring->cycle_state = (ring->cycle_state ? 0 : 1);
+                        if (!in_interrupt())
+                                xhci_dbg(xhci, "Toggle cycle state for ring 0x%x = %i\n",
+                                                (unsigned int) ring,
+                                                (unsigned int) ring->cycle_state);
+                }
+                ring->deq_seg = ring->deq_seg->next;
+                ring->dequeue = ring->deq_seg->trbs;
+                next = ring->dequeue;
+        }
+}
+
+/*
+ * See Cycle bit rules. SW is the consumer for the event ring only.
+ * Don't make a ring full of link TRBs.  That would be dumb and this would loop.
+ *
+ * If we've just enqueued a TRB that is in the middle of a TD (meaning the
+ * chain bit is set), then set the chain bit in all the following link TRBs.
+ * If we've enqueued the last TRB in a TD, make sure the following link TRBs
+ * have their chain bit cleared (so that each Link TRB is a separate TD).
+ *
+ * Section 6.4.4.1 of the 0.95 spec says link TRBs cannot have the chain bit
+ * set, but other sections talk about dealing with the chain bit set.
+ * Assume section 6.4.4.1 is wrong, and the chain bit can be set in a Link TRB.
+ */
+static void inc_enq(struct xhci_hcd *xhci, struct xhci_ring *ring, bool consumer)
+{
+        u32 chain;
+        union xhci_trb *next;
+
+        chain = ring->enqueue->generic.field[3] & TRB_CHAIN;
+        next = ++(ring->enqueue);
+
+        ring->enq_updates++;
+        /* Update the dequeue pointer further if that was a link TRB or we're at
+         * the end of an event ring segment (which doesn't have link TRBS)
+         */
+        while (last_trb(xhci, ring, ring->enq_seg, next)) {
+                if (!consumer) {
+                        if (ring != xhci->event_ring) {
+                                /* Give this link TRB to the hardware */
+                                if (next->link.control & TRB_CYCLE)
+                                        next->link.control &= (u32) ~TRB_CYCLE;
+                                else
+                                        next->link.control |= (u32) TRB_CYCLE;
+                                next->link.control &= TRB_CHAIN;
+                                next->link.control |= chain;
+                        }
+                        /* Toggle the cycle bit after the last ring segment. */
+                        if (last_trb_on_last_seg(xhci, ring, ring->enq_seg, next)) {
+                                ring->cycle_state = (ring->cycle_state ? 0 : 1);
+                                if (!in_interrupt())
+                                        xhci_dbg(xhci, "Toggle cycle state for ring 0x%x = %i\n",
+                                                        (unsigned int) ring,
+                                                        (unsigned int) ring->cycle_state);
+                        }
+                }
+                ring->enq_seg = ring->enq_seg->next;
+                ring->enqueue = ring->enq_seg->trbs;
+                next = ring->enqueue;
+        }
+}
+
+/*
+ * Check to see if there's room to enqueue num_trbs on the ring.  See rules
+ * above.
+ * FIXME: this would be simpler and faster if we just kept track of the number
+ * of free TRBs in a ring.
+ */
+static int room_on_ring(struct xhci_hcd *xhci, struct xhci_ring *ring,
+                unsigned int num_trbs)
+{
+        int i;
+        union xhci_trb *enq = ring->enqueue;
+        struct xhci_segment *enq_seg = ring->enq_seg;
+
+        /* Check if ring is empty */
+        if (enq == ring->dequeue)
+                return 1;
+        /* Make sure there's an extra empty TRB available */
+        for (i = 0; i <= num_trbs; ++i) {
+                if (enq == ring->dequeue)
+                        return 0;
+                enq++;
+                while (last_trb(xhci, ring, enq_seg, enq)) {
+                        enq_seg = enq_seg->next;
+                        enq = enq_seg->trbs;
+                }
+        }
+        return 1;
+}
+
+void set_hc_event_deq(struct xhci_hcd *xhci)
+{
+        u32 temp;
+        dma_addr_t deq;
+
+        deq = trb_virt_to_dma(xhci->event_ring->deq_seg,
+                        xhci->event_ring->dequeue);
+        if (deq == 0 && !in_interrupt())
+                xhci_warn(xhci, "WARN something wrong with SW event ring "
+                                "dequeue ptr.\n");
+        /* Update HC event ring dequeue pointer */
+        temp = xhci_readl(xhci, &xhci->ir_set->erst_dequeue[0]);
+        temp &= ERST_PTR_MASK;
+        if (!in_interrupt())
+                xhci_dbg(xhci, "// Write event ring dequeue pointer\n");
+        xhci_writel(xhci, 0, &xhci->ir_set->erst_dequeue[1]);
+        xhci_writel(xhci, (deq & ~ERST_PTR_MASK) | temp,
+                        &xhci->ir_set->erst_dequeue[0]);
+}
+
+/* Ring the host controller doorbell after placing a command on the ring */
+void ring_cmd_db(struct xhci_hcd *xhci)
+{
+        u32 temp;
+
+        xhci_dbg(xhci, "// Ding dong!\n");
+        temp = xhci_readl(xhci, &xhci->dba->doorbell[0]) & DB_MASK;
+        xhci_writel(xhci, temp | DB_TARGET_HOST, &xhci->dba->doorbell[0]);
+        /* Flush PCI posted writes */
+        xhci_readl(xhci, &xhci->dba->doorbell[0]);
+}
+
+static void handle_cmd_completion(struct xhci_hcd *xhci,
+                struct xhci_event_cmd *event)
+{
+        u64 cmd_dma;
+        dma_addr_t cmd_dequeue_dma;
+
+        /* Check completion code */
+        if (GET_COMP_CODE(event->status) != COMP_SUCCESS)
+                xhci_dbg(xhci, "WARN: unsuccessful no-op command\n");
+
+        cmd_dma = (((u64) event->cmd_trb[1]) << 32) + event->cmd_trb[0];
+        cmd_dequeue_dma = trb_virt_to_dma(xhci->cmd_ring->deq_seg,
+                        xhci->cmd_ring->dequeue);
+        /* Is the command ring deq ptr out of sync with the deq seg ptr? */
+        if (cmd_dequeue_dma == 0) {
+                xhci->error_bitmask |= 1 << 4;
+                return;
+        }
+        /* Does the DMA address match our internal dequeue pointer address? */
+        if (cmd_dma != (u64) cmd_dequeue_dma) {
+                xhci->error_bitmask |= 1 << 5;
+                return;
+        }
+        switch (xhci->cmd_ring->dequeue->generic.field[3] & TRB_TYPE_BITMASK) {
+        case TRB_TYPE(TRB_CMD_NOOP):
+                ++xhci->noops_handled;
+                break;
+        default:
+                /* Skip over unknown commands on the event ring */
+                xhci->error_bitmask |= 1 << 6;
+                break;
+        }
+        inc_deq(xhci, xhci->cmd_ring, false);
+}
+
+void handle_event(struct xhci_hcd *xhci)
+{
+        union xhci_trb *event;
+
+        if (!xhci->event_ring || !xhci->event_ring->dequeue) {
+                xhci->error_bitmask |= 1 << 1;
+                return;
+        }
+
+        event = xhci->event_ring->dequeue;
+        /* Does the HC or OS own the TRB? */
+        if ((event->event_cmd.flags & TRB_CYCLE) !=
+                        xhci->event_ring->cycle_state) {
+                xhci->error_bitmask |= 1 << 2;
+                return;
+        }
+
+        /* FIXME: Only handles command completion events. */
+        switch ((event->event_cmd.flags & TRB_TYPE_BITMASK)) {
+        case TRB_TYPE(TRB_COMPLETION):
+                handle_cmd_completion(xhci, &event->event_cmd);
+                break;
+        default:
+                xhci->error_bitmask |= 1 << 3;
+        }
+
+        /* Update SW and HC event ring dequeue pointer */
+        inc_deq(xhci, xhci->event_ring, true);
+        set_hc_event_deq(xhci);
+        /* Are there more items on the event ring? */
+        handle_event(xhci);
+}
+
+/*
+ * Generic function for queueing a TRB on a ring.
+ * The caller must have checked to make sure there's room on the ring.
+ */
+static void queue_trb(struct xhci_hcd *xhci, struct xhci_ring *ring,
+                bool consumer,
+                u32 field1, u32 field2, u32 field3, u32 field4)
+{
+        struct xhci_generic_trb *trb;
+
+        trb = &ring->enqueue->generic;
+        trb->field[0] = field1;
+        trb->field[1] = field2;
+        trb->field[2] = field3;
+        trb->field[3] = field4;
+        inc_enq(xhci, ring, consumer);
+}
+
+/* Generic function for queueing a command TRB on the command ring */
+static int queue_command(struct xhci_hcd *xhci, u32 field1, u32 field2, u32 field3, u32 field4)
+{
+        if (!room_on_ring(xhci, xhci->cmd_ring, 1)) {
+                if (!in_interrupt())
+                        xhci_err(xhci, "ERR: No room for command on command ring\n");
+                return -ENOMEM;
+        }
+        queue_trb(xhci, xhci->cmd_ring, false, field1, field2, field3,
+                        field4 | xhci->cmd_ring->cycle_state);
+        return 0;
+}
+
+/* Queue a no-op command on the command ring */
+static int queue_cmd_noop(struct xhci_hcd *xhci)
+{
+        return queue_command(xhci, 0, 0, 0, TRB_TYPE(TRB_CMD_NOOP));
+}
+
+/*
+ * Place a no-op command on the command ring to test the command and
+ * event ring.
+ */
+void *setup_one_noop(struct xhci_hcd *xhci)
+{
+        if (queue_cmd_noop(xhci) < 0)
+                return NULL;
+        xhci->noops_submitted++;
+        return ring_cmd_db;
+}
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index f168fcac5999..66be134b8921 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -24,6 +24,7 @@
 #define __LINUX_XHCI_HCD_H
 
 #include <linux/usb.h>
+#include <linux/timer.h>
 
 #include "../core/hcd.h"
 /* Code sharing between pci-quirks and xhci hcd */
@@ -377,6 +378,7 @@ struct intr_reg {
 /* irq_pending bitmasks */
 #define ER_IRQ_PENDING(p)       ((p) & 0x1)
 /* bits 2:31 need to be preserved */
+/* THIS IS BUGGY - FIXME - IP IS WRITE 1 TO CLEAR */
 #define ER_IRQ_CLEAR(p)         ((p) & 0xfffffffe)
 #define ER_IRQ_ENABLE(p)        ((ER_IRQ_CLEAR(p)) | 0x2)
 #define ER_IRQ_DISABLE(p)       ((ER_IRQ_CLEAR(p)) & ~(0x2))
@@ -699,11 +701,14 @@ struct xhci_link_trb {
 /* control bitfields */
 #define LINK_TOGGLE     (0x1<<1)
 
+/* Command completion event TRB */
+struct xhci_event_cmd {
+        /* Pointer to command TRB, or the value passed by the event data trb */
+        u32 cmd_trb[2];
+        u32 status;
+        u32 flags;
+} __attribute__ ((packed));
 
-union xhci_trb {
-        struct xhci_link_trb            link;
-        struct xhci_transfer_event      trans_event;
-};
 
 /* Normal TRB fields */
 /* transfer_len bitmasks - bits 0:16 */
@@ -737,6 +742,17 @@ union xhci_trb {
 /* Control transfer TRB specific fields */
 #define TRB_DIR_IN              (1<<16)
 
+struct xhci_generic_trb {
+        u32 field[4];
+} __attribute__ ((packed));
+
+union xhci_trb {
+        struct xhci_link_trb            link;
+        struct xhci_transfer_event      trans_event;
+        struct xhci_event_cmd           event_cmd;
+        struct xhci_generic_trb         generic;
+};
+
 /* TRB bit mask */
 #define TRB_TYPE_BITMASK        (0xfc00)
 #define TRB_TYPE(p)             ((p) << 10)
@@ -825,7 +841,11 @@ struct xhci_segment {
 struct xhci_ring {
         struct xhci_segment     *first_seg;
         union  xhci_trb         *enqueue;
+        struct xhci_segment     *enq_seg;
+        unsigned int            enq_updates;
         union  xhci_trb         *dequeue;
+        struct xhci_segment     *deq_seg;
+        unsigned int            deq_updates;
         /*
          * Write the cycle state into the TRB cycle field to give ownership of
          * the TRB to the host controller (if we are the producer), or to check
@@ -861,6 +881,8 @@ struct xhci_erst {
 #define ERST_SIZE       64
 /* Initial number of event segment rings allocated */
 #define ERST_ENTRIES    1
+/* Poll every 60 seconds */
+#define POLL_TIMEOUT    60
 /* XXX: Make these module parameters */
 
 
@@ -907,8 +929,21 @@ struct xhci_hcd {
         /* DMA pools */
         struct dma_pool *device_pool;
         struct dma_pool *segment_pool;
+
+#ifdef CONFIG_USB_XHCI_HCD_DEBUGGING
+        /* Poll the rings - for debugging */
+        struct timer_list       event_ring_timer;
+        int                     zombie;
+#endif
+        /* Statistics */
+        int                     noops_submitted;
+        int                     noops_handled;
+        int                     error_bitmask;
 };
 
+/* For testing purposes */
+#define NUM_TEST_NOOPS  0
+
 /* convert between an HCD pointer and the corresponding EHCI_HCD */
 static inline struct xhci_hcd *hcd_to_xhci(struct usb_hcd *hcd)
 {
@@ -956,9 +991,11 @@ void xhci_print_ir_set(struct xhci_hcd *xhci, struct intr_reg *ir_set, int set_n
 void xhci_print_registers(struct xhci_hcd *xhci);
 void xhci_dbg_regs(struct xhci_hcd *xhci);
 void xhci_print_run_regs(struct xhci_hcd *xhci);
+void xhci_debug_segment(struct xhci_hcd *xhci, struct xhci_segment *seg);
 void xhci_debug_ring(struct xhci_hcd *xhci, struct xhci_ring *ring);
 void xhci_dbg_erst(struct xhci_hcd *xhci, struct xhci_erst *erst);
 void xhci_dbg_cmd_ptrs(struct xhci_hcd *xhci);
+void xhci_dbg_ring_ptrs(struct xhci_hcd *xhci, struct xhci_ring *ring);
 
 /* xHCI memory managment */
 void xhci_mem_cleanup(struct xhci_hcd *xhci);
@@ -978,5 +1015,13 @@ int xhci_run(struct usb_hcd *hcd);
 void xhci_stop(struct usb_hcd *hcd);
 void xhci_shutdown(struct usb_hcd *hcd);
 int xhci_get_frame(struct usb_hcd *hcd);
+irqreturn_t xhci_irq(struct usb_hcd *hcd);
+
+/* xHCI ring, segment, TRB, and TD functions */
+dma_addr_t trb_virt_to_dma(struct xhci_segment *seg, union xhci_trb *trb);
+void ring_cmd_db(struct xhci_hcd *xhci);
+void *setup_one_noop(struct xhci_hcd *xhci);
+void handle_event(struct xhci_hcd *xhci);
+void set_hc_event_deq(struct xhci_hcd *xhci);
 
 #endif /* __LINUX_XHCI_HCD_H */