USB: EHCI: use hrtimer for interrupt QH unlink

This patch (as1577) adds hrtimer support for unlinking interrupt QHs
in ehci-hcd.  The current code relies on a fixed delay of either 2 or
55 us, which is not always adequate and in any case is totally bogus.
Thanks to internal caching, the EHCI hardware may continue to access
an interrupt QH for more than a millisecond after it has been unlinked.

In fact, the EHCI spec doesn't say how long to wait before using an
unlinked interrupt QH.  The patch sets the delay to 9 microframes
minimum, which ought to be adequate.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

5 files changed, 94 insertions, 28 deletions

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 21d6fbc0a327..edcfd2c4295e 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -309,6 +309,8 @@ static void ehci_quiesce (struct ehci_hcd *ehci)
 
 static void end_unlink_async(struct ehci_hcd *ehci);
 static void ehci_work(struct ehci_hcd *ehci);
+static void start_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);
+static void end_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh);
 
 #include "ehci-timer.c"
 #include "ehci-hub.c"
@@ -1034,7 +1036,7 @@ static int ehci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
                 switch (qh->qh_state) {
                 case QH_STATE_LINKED:
                 case QH_STATE_COMPLETING:
-                        intr_deschedule (ehci, qh);
+                        start_unlink_intr(ehci, qh);
                         break;
                 case QH_STATE_IDLE:
                         qh_completions (ehci, qh);
@@ -1164,7 +1166,7 @@ ehci_endpoint_reset(struct usb_hcd *hcd, struct usb_host_endpoint *ep)
                         if (eptype == USB_ENDPOINT_XFER_BULK)
                                 unlink_async(ehci, qh);
                         else
-                                intr_deschedule(ehci, qh);
+                                start_unlink_intr(ehci, qh);
                 }
         }
         spin_unlock_irqrestore(&ehci->lock, flags);
diff --git a/drivers/usb/host/ehci-hub.c b/drivers/usb/host/ehci-hub.c
index 25329e4b844f..8aa740dc510d 100644
--- a/drivers/usb/host/ehci-hub.c
+++ b/drivers/usb/host/ehci-hub.c
@@ -302,6 +302,7 @@ static int ehci_bus_suspend (struct usb_hcd *hcd)
 
         if (ehci->async_unlink)
                 end_unlink_async(ehci);
+        ehci_handle_intr_unlinks(ehci);
 
         /* allow remote wakeup */
         mask = INTR_MASK;
diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index 69b1861e4325..eec8446f8ded 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -578,12 +578,20 @@ static void qh_unlink_periodic(struct ehci_hcd *ehci, struct ehci_qh *qh)
         unsigned        i;
         unsigned        period;
 
-        // FIXME:
-        // IF this isn't high speed
-        //   and this qh is active in the current uframe
-        //   (and overlay token SplitXstate is false?)
-        // THEN
-        //   qh->hw_info1 |= cpu_to_hc32(1 << 7 /* "ignore" */);
+        /*
+         * If qh is for a low/full-speed device, simply unlinking it
+         * could interfere with an ongoing split transaction.  To unlink
+         * it safely would require setting the QH_INACTIVATE bit and
+         * waiting at least one frame, as described in EHCI 4.12.2.5.
+         *
+         * We won't bother with any of this.  Instead, we assume that the
+         * only reason for unlinking an interrupt QH while the current URB
+         * is still active is to dequeue all the URBs (flush the whole
+         * endpoint queue).
+         *
+         * If rebalancing the periodic schedule is ever implemented, this
+         * approach will no longer be valid.
+         */
 
         /* high bandwidth, or otherwise part of every microframe */
         if ((period = qh->period) == 0)
@@ -608,12 +616,8 @@ static void qh_unlink_periodic(struct ehci_hcd *ehci, struct ehci_qh *qh)
         qh->qh_next.ptr = NULL;
 }
 
-static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
+static void start_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh)
 {
-        unsigned                wait;
-        struct ehci_qh_hw       *hw = qh->hw;
-        int                     rc;
-
         /* If the QH isn't linked then there's nothing we can do
          * unless we were called during a giveback, in which case
          * qh_completions() has to deal with it.
@@ -626,28 +630,45 @@ static void intr_deschedule (struct ehci_hcd *ehci, struct ehci_qh *qh)
 
         qh_unlink_periodic (ehci, qh);
 
-        /* simple/paranoid:  always delay, expecting the HC needs to read
-         * qh->hw_next or finish a writeback after SPLIT/CSPLIT ... and
-         * expect khubd to clean up after any CSPLITs we won't issue.
-         * active high speed queues may need bigger delays...
+        /* Make sure the unlinks are visible before starting the timer */
+        wmb();
+
+        /*
+         * The EHCI spec doesn't say how long it takes the controller to
+         * stop accessing an unlinked interrupt QH.  The timer delay is
+         * 9 uframes; presumably that will be long enough.
          */
-        if (list_empty (&qh->qtd_list)
-                        || (cpu_to_hc32(ehci, QH_CMASK)
-                                        & hw->hw_info2) != 0)
-                wait = 2;
+        qh->unlink_cycle = ehci->intr_unlink_cycle;
+
+        /* New entries go at the end of the intr_unlink list */
+        if (ehci->intr_unlink)
+                ehci->intr_unlink_last->unlink_next = qh;
         else
-                wait = 55;      /* worst case: 3 * 1024 */
+                ehci->intr_unlink = qh;
+        ehci->intr_unlink_last = qh;
+
+        if (ehci->intr_unlinking)
+                ;       /* Avoid recursive calls */
+        else if (ehci->rh_state < EHCI_RH_RUNNING)
+                ehci_handle_intr_unlinks(ehci);
+        else if (ehci->intr_unlink == qh) {
+                ehci_enable_event(ehci, EHCI_HRTIMER_UNLINK_INTR, true);
+                ++ehci->intr_unlink_cycle;
+        }
+}
+
+static void end_unlink_intr(struct ehci_hcd *ehci, struct ehci_qh *qh)
+{
+        struct ehci_qh_hw       *hw = qh->hw;
+        int                     rc;
 
-        udelay (wait);
         qh->qh_state = QH_STATE_IDLE;
         hw->hw_next = EHCI_LIST_END(ehci);
-        wmb ();
 
         qh_completions(ehci, qh);
 
         /* reschedule QH iff another request is queued */
-        if (!list_empty(&qh->qtd_list) &&
-                        ehci->rh_state == EHCI_RH_RUNNING) {
+        if (!list_empty(&qh->qtd_list) && ehci->rh_state == EHCI_RH_RUNNING) {
                 rc = qh_schedule(ehci, qh);
 
                 /* An error here likely indicates handshake failure
@@ -2302,7 +2323,7 @@ restart:
                                                 temp.qh->stamp = ehci->periodic_stamp;
                                         if (unlikely(list_empty(&temp.qh->qtd_list) ||
                                                         temp.qh->needs_rescan))
-                                                intr_deschedule(ehci, temp.qh);
+                                                start_unlink_intr(ehci, temp.qh);
                                 }
                                 break;
                         case Q_TYPE_FSTN:
diff --git a/drivers/usb/host/ehci-timer.c b/drivers/usb/host/ehci-timer.c
index 1e907dd3bb1b..bd8b591771b0 100644
--- a/drivers/usb/host/ehci-timer.c
+++ b/drivers/usb/host/ehci-timer.c
@@ -69,6 +69,7 @@ static void ehci_clear_command_bit(struct ehci_hcd *ehci, u32 bit)
 static unsigned event_delays_ns[] = {
         1 * NSEC_PER_MSEC,      /* EHCI_HRTIMER_POLL_ASS */
         1 * NSEC_PER_MSEC,      /* EHCI_HRTIMER_POLL_PSS */
+        1125 * NSEC_PER_USEC,   /* EHCI_HRTIMER_UNLINK_INTR */
         10 * NSEC_PER_MSEC,     /* EHCI_HRTIMER_DISABLE_PERIODIC */
         15 * NSEC_PER_MSEC,     /* EHCI_HRTIMER_DISABLE_ASYNC */
 };
@@ -192,6 +193,38 @@ static void ehci_disable_PSE(struct ehci_hcd *ehci)
 }
 
 
+/* Handle unlinked interrupt QHs once they are gone from the hardware */
+static void ehci_handle_intr_unlinks(struct ehci_hcd *ehci)
+{
+        bool            stopped = (ehci->rh_state < EHCI_RH_RUNNING);
+
+        /*
+         * Process all the QHs on the intr_unlink list that were added
+         * before the current unlink cycle began.  The list is in
+         * temporal order, so stop when we reach the first entry in the
+         * current cycle.  But if the root hub isn't running then
+         * process all the QHs on the list.
+         */
+        ehci->intr_unlinking = true;
+        while (ehci->intr_unlink) {
+                struct ehci_qh  *qh = ehci->intr_unlink;
+
+                if (!stopped && qh->unlink_cycle == ehci->intr_unlink_cycle)
+                        break;
+                ehci->intr_unlink = qh->unlink_next;
+                qh->unlink_next = NULL;
+                end_unlink_intr(ehci, qh);
+        }
+
+        /* Handle remaining entries later */
+        if (ehci->intr_unlink) {
+                ehci_enable_event(ehci, EHCI_HRTIMER_UNLINK_INTR, true);
+                ++ehci->intr_unlink_cycle;
+        }
+        ehci->intr_unlinking = false;
+}
+
+
 /*
  * Handler functions for the hrtimer event types.
  * Keep this array in the same order as the event types indexed by
@@ -200,6 +233,7 @@ static void ehci_disable_PSE(struct ehci_hcd *ehci)
 static void (*event_handlers[])(struct ehci_hcd *) = {
         ehci_poll_ASS,                  /* EHCI_HRTIMER_POLL_ASS */
         ehci_poll_PSS,                  /* EHCI_HRTIMER_POLL_PSS */
+        ehci_handle_intr_unlinks,       /* EHCI_HRTIMER_UNLINK_INTR */
         ehci_disable_PSE,               /* EHCI_HRTIMER_DISABLE_PERIODIC */
         ehci_disable_ASE,               /* EHCI_HRTIMER_DISABLE_ASYNC */
 };
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index bf06bbb77ba4..f36f1f85d7fd 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -81,6 +81,7 @@ enum ehci_rh_state {
 enum ehci_hrtimer_event {
         EHCI_HRTIMER_POLL_ASS,          /* Poll for async schedule off */
         EHCI_HRTIMER_POLL_PSS,          /* Poll for periodic schedule off */
+        EHCI_HRTIMER_UNLINK_INTR,       /* Wait for interrupt QH unlink */
         EHCI_HRTIMER_DISABLE_PERIODIC,  /* Wait to disable periodic sched */
         EHCI_HRTIMER_DISABLE_ASYNC,     /* Wait to disable async sched */
         EHCI_HRTIMER_NUM_EVENTS         /* Must come last */
@@ -106,13 +107,16 @@ struct ehci_hcd {			/* one per controller */
         spinlock_t              lock;
         enum ehci_rh_state      rh_state;
 
+        /* general schedule support */
+        unsigned                scanning:1;
+        bool                    intr_unlinking:1;
+
         /* async schedule support */
         struct ehci_qh          *async;
         struct ehci_qh          *dummy;         /* For AMD quirk use */
         struct ehci_qh          *async_unlink;
         struct ehci_qh          *async_unlink_last;
         struct ehci_qh          *qh_scan_next;
-        unsigned                scanning : 1;
         unsigned                async_count;    /* async activity count */
 
         /* periodic schedule support */
@@ -123,6 +127,9 @@ struct ehci_hcd {			/* one per controller */
         unsigned                i_thresh;       /* uframes HC might cache */
 
         union ehci_shadow       *pshadow;       /* mirror hw periodic table */
+        struct ehci_qh          *intr_unlink;
+        struct ehci_qh          *intr_unlink_last;
+        unsigned                intr_unlink_cycle;
         int                     next_uframe;    /* scan periodic, start here */
         unsigned                periodic_count; /* periodic activity count */
         unsigned                uframe_periodic_max; /* max periodic time per uframe */
@@ -385,6 +392,7 @@ struct ehci_qh {
         struct ehci_qh          *unlink_next;   /* next on unlink list */
 
         unsigned long           unlink_time;
+        unsigned                unlink_cycle;
         unsigned                stamp;
 
         u8                      needs_rescan;   /* Dequeue during giveback */