[PATCH] usb: dwc2: host: use hrtimer for NAK retries

[Terin Stock <terin@xxxxxxxxxxxxxx>]

Upon upgrading a Raspberry Pi 3B-based project from vanilla 4.14,
attempts to mount a floppy disk in a generic USB floppy drive would hang
until the floppy drive was removed from the system.

Tracing shows that during mounting the drive produces a large amount of
NAKed transactions, but would eventually continue. A previous commit
added a retry delay on NAKed transactions, using jiffies, that results
in indefinite NAKs in this scenario.

Modify the wait delay utilize the high resolution timer API to allow for
more accurately scheduled callbacks.

Fixes: 38d2b5fb75c1 ("usb: dwc2: host: Don't retry NAKed transactions right away")
Signed-off-by: Terin Stock <terin@xxxxxxxxxxxxxx>
---
 drivers/usb/dwc2/hcd.h       |    2 +-
 drivers/usb/dwc2/hcd_queue.c |   17 ++++++++++-------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/usb/dwc2/hcd.h b/drivers/usb/dwc2/hcd.h
index 5502a501f516..93483dc37801 100644
--- a/drivers/usb/dwc2/hcd.h
+++ b/drivers/usb/dwc2/hcd.h
@@ -366,7 +366,7 @@ struct dwc2_qh {
 	u32 desc_list_sz;
 	u32 *n_bytes;
 	struct timer_list unreserve_timer;
-	struct timer_list wait_timer;
+	struct hrtimer wait_timer;
 	struct dwc2_tt *dwc_tt;
 	int ttport;
 	unsigned tt_buffer_dirty:1;
diff --git a/drivers/usb/dwc2/hcd_queue.c b/drivers/usb/dwc2/hcd_queue.c
index 301ced1618f8..2d0cfd7f2cfe 100644
--- a/drivers/usb/dwc2/hcd_queue.c
+++ b/drivers/usb/dwc2/hcd_queue.c
@@ -59,7 +59,7 @@
 #define DWC2_UNRESERVE_DELAY (msecs_to_jiffies(5))
 
 /* If we get a NAK, wait this long before retrying */
-#define DWC2_RETRY_WAIT_DELAY (msecs_to_jiffies(1))
+#define DWC2_RETRY_WAIT_DELAY 1*1E6L
 
 /**
  * dwc2_periodic_channel_available() - Checks that a channel is available for a
@@ -1465,9 +1465,9 @@ static void dwc2_deschedule_periodic(struct dwc2_hsotg *hsotg,
  *
  * @t: Pointer to wait_timer in a qh.
  */
-static void dwc2_wait_timer_fn(struct timer_list *t)
+static enum hrtimer_restart dwc2_wait_timer_fn(struct hrtimer *t)
 {
-	struct dwc2_qh *qh = from_timer(qh, t, wait_timer);
+	struct dwc2_qh *qh = container_of(t, struct dwc2_qh, wait_timer);
 	struct dwc2_hsotg *hsotg = qh->hsotg;
 	unsigned long flags;
 
@@ -1491,6 +1491,7 @@ static void dwc2_wait_timer_fn(struct timer_list *t)
 	}
 
 	spin_unlock_irqrestore(&hsotg->lock, flags);
+	return HRTIMER_NORESTART;
 }
 
 /**
@@ -1521,7 +1522,8 @@ static void dwc2_qh_init(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
 	/* Initialize QH */
 	qh->hsotg = hsotg;
 	timer_setup(&qh->unreserve_timer, dwc2_unreserve_timer_fn, 0);
-	timer_setup(&qh->wait_timer, dwc2_wait_timer_fn, 0);
+	hrtimer_init(&qh->wait_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	qh->wait_timer.function = &dwc2_wait_timer_fn;
 	qh->ep_type = ep_type;
 	qh->ep_is_in = ep_is_in;
 
@@ -1690,7 +1692,7 @@ void dwc2_hcd_qh_free(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 	 * won't do anything anyway, but we want it to finish before we free
 	 * memory.
 	 */
-	del_timer_sync(&qh->wait_timer);
+	hrtimer_cancel(&qh->wait_timer);
 
 	dwc2_host_put_tt_info(hsotg, qh->dwc_tt);
 
@@ -1716,6 +1718,7 @@ int dwc2_hcd_qh_add(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 {
 	int status;
 	u32 intr_mask;
+	ktime_t delay;
 
 	if (dbg_qh(qh))
 		dev_vdbg(hsotg->dev, "%s()\n", __func__);
@@ -1734,8 +1737,8 @@ int dwc2_hcd_qh_add(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 			list_add_tail(&qh->qh_list_entry,
 				      &hsotg->non_periodic_sched_waiting);
 			qh->wait_timer_cancel = false;
-			mod_timer(&qh->wait_timer,
-				  jiffies + DWC2_RETRY_WAIT_DELAY + 1);
+			delay = ktime_set(0, DWC2_RETRY_WAIT_DELAY);
+			hrtimer_start(&qh->wait_timer, delay, HRTIMER_MODE_REL);
 		} else {
 			list_add_tail(&qh->qh_list_entry,
 				      &hsotg->non_periodic_sched_inactive);