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>

1 files changed, 46 insertions, 25 deletions

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: