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@@ -58,6 +58,9 @@
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/* Wait this long before releasing periodic reservation */
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#define DWC2_UNRESERVE_DELAY (msecs_to_jiffies(5))
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+/* If we get a NAK, wait this long before retrying */
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+#define DWC2_RETRY_WAIT_DELAY (msecs_to_jiffies(1))
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+
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/**
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* dwc2_periodic_channel_available() - Checks that a channel is available for a
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* periodic transfer
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@@ -1440,6 +1443,55 @@ static void dwc2_deschedule_periodic(struct dwc2_hsotg *hsotg,
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list_del_init(&qh->qh_list_entry);
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}
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+/**
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+ * dwc2_wait_timer_fn() - Timer function to re-queue after waiting
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+ *
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+ * As per the spec, a NAK indicates that "a function is temporarily unable to
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+ * transmit or receive data, but will eventually be able to do so without need
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+ * of host intervention".
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+ *
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+ * That means that when we encounter a NAK we're supposed to retry.
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+ *
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+ * ...but if we retry right away (from the interrupt handler that saw the NAK)
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+ * then we can end up with an interrupt storm (if the other side keeps NAKing
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+ * us) because on slow enough CPUs it could take us longer to get out of the
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+ * interrupt routine than it takes for the device to send another NAK. That
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+ * leads to a constant stream of NAK interrupts and the CPU locks.
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+ *
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+ * ...so instead of retrying right away in the case of a NAK we'll set a timer
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+ * to retry some time later. This function handles that timer and moves the
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+ * qh back to the "inactive" list, then queues transactions.
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+ *
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+ * @t: Pointer to wait_timer in a qh.
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+ */
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+static void dwc2_wait_timer_fn(struct timer_list *t)
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+{
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+ struct dwc2_qh *qh = from_timer(qh, t, wait_timer);
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+ struct dwc2_hsotg *hsotg = qh->hsotg;
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+ unsigned long flags;
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+
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+ spin_lock_irqsave(&hsotg->lock, flags);
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+
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+ /*
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+ * We'll set wait_timer_cancel to true if we want to cancel this
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+ * operation in dwc2_hcd_qh_unlink().
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+ */
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+ if (!qh->wait_timer_cancel) {
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+ enum dwc2_transaction_type tr_type;
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+
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+ qh->want_wait = false;
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+
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+ list_move(&qh->qh_list_entry,
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+ &hsotg->non_periodic_sched_inactive);
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+
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+ tr_type = dwc2_hcd_select_transactions(hsotg);
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+ if (tr_type != DWC2_TRANSACTION_NONE)
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+ dwc2_hcd_queue_transactions(hsotg, tr_type);
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+ }
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+
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+ spin_unlock_irqrestore(&hsotg->lock, flags);
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+}
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+
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/**
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* dwc2_qh_init() - Initializes a QH structure
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*
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@@ -1468,6 +1520,7 @@ static void dwc2_qh_init(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
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/* Initialize QH */
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qh->hsotg = hsotg;
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timer_setup(&qh->unreserve_timer, dwc2_unreserve_timer_fn, 0);
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+ timer_setup(&qh->wait_timer, dwc2_wait_timer_fn, 0);
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qh->ep_type = ep_type;
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qh->ep_is_in = ep_is_in;
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@@ -1628,6 +1681,16 @@ void dwc2_hcd_qh_free(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
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dwc2_do_unreserve(hsotg, qh);
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spin_unlock_irqrestore(&hsotg->lock, flags);
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}
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+
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+ /*
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+ * We don't have the lock so we can safely wait until the wait timer
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+ * finishes. Of course, at this point in time we'd better have set
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+ * wait_timer_active to false so if this timer was still pending it
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+ * won't do anything anyway, but we want it to finish before we free
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+ * memory.
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+ */
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+ del_timer_sync(&qh->wait_timer);
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+
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dwc2_host_put_tt_info(hsotg, qh->dwc_tt);
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if (qh->desc_list)
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@@ -1663,9 +1726,16 @@ int dwc2_hcd_qh_add(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
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qh->start_active_frame = hsotg->frame_number;
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qh->next_active_frame = qh->start_active_frame;
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- /* Always start in inactive schedule */
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- list_add_tail(&qh->qh_list_entry,
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- &hsotg->non_periodic_sched_inactive);
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+ if (qh->want_wait) {
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+ list_add_tail(&qh->qh_list_entry,
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+ &hsotg->non_periodic_sched_waiting);
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+ qh->wait_timer_cancel = false;
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+ mod_timer(&qh->wait_timer,
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+ jiffies + DWC2_RETRY_WAIT_DELAY + 1);
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+ } else {
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+ list_add_tail(&qh->qh_list_entry,
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+ &hsotg->non_periodic_sched_inactive);
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+ }
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return 0;
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}
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@@ -1695,6 +1765,9 @@ void dwc2_hcd_qh_unlink(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
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dev_vdbg(hsotg->dev, "%s()\n", __func__);
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+ /* If the wait_timer is pending, this will stop it from acting */
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+ qh->wait_timer_cancel = true;
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+
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if (list_empty(&qh->qh_list_entry))
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/* QH is not in a schedule */
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return;
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@@ -1903,7 +1976,7 @@ void dwc2_hcd_qh_deactivate(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
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if (dwc2_qh_is_non_per(qh)) {
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dwc2_hcd_qh_unlink(hsotg, qh);
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if (!list_empty(&qh->qtd_list))
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- /* Add back to inactive non-periodic schedule */
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+ /* Add back to inactive/waiting non-periodic schedule */
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dwc2_hcd_qh_add(hsotg, qh);
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return;
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}
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Douglas Anderson