[PATCH v2] usb: dwc2: host: use hrtimer for NAK retries

[Terin Stock]

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

A previous commit added a 1ms retry delay after multiple consecutive
NAKed transactions using jiffies. On systems with a low timer interrupt
frequency, this delay may be significantly longer than specified,
resulting in misbehavior with some USB devices.

This scenario was reached on a Raspberry Pi 3B with a Macally FDD-USB
floppy drive (identified as 0424:0fdc Standard Microsystems Corp.
Floppy, based on the USB97CFDC USB FDC). With the relay delay, the drive
would be unable to mount a disk, replying with NAKs until the device was
reset.

Using ktime, the delta between starting the timer (in dwc2_hcd_qh_add)
and the callback function can be determined. With the original delay
implementation, this value was consistently approximately 12ms. (output
in us).

    <idle>-0     [000] ..s.  1600.559974: dwc2_wait_timer_fn: wait_timer delta: 11976
    <idle>-0     [000] ..s.  1600.571974: dwc2_wait_timer_fn: wait_timer delta: 11977
    <idle>-0     [000] ..s.  1600.583974: dwc2_wait_timer_fn: wait_timer delta: 11976
    <idle>-0     [000] ..s.  1600.595974: dwc2_wait_timer_fn: wait_timer delta: 11977

After converting the relay delay to using a higher resolution timer, the
delay was much closer to 1ms.

    <idle>-0     [000] d.h.  1956.553017: dwc2_wait_timer_fn: wait_timer delta: 1002
    <idle>-0     [000] d.h.  1956.554114: dwc2_wait_timer_fn: wait_timer delta: 1002
    <idle>-0     [000] d.h.  1957.542660: dwc2_wait_timer_fn: wait_timer delta: 1004
    <idle>-0     [000] d.h.  1957.543701: dwc2_wait_timer_fn: wait_timer delta: 1002

The floppy drive operates properly with delays up to approximately 5ms,
and sends NAKs for any delays that are longer.

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 |   19 ++++++++++++-------
 2 files changed, 13 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..60caf8e0b762 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
@@ -1464,10 +1464,12 @@ static void dwc2_deschedule_periodic(struct dwc2_hsotg *hsotg,
  * qh back to the "inactive" list, then queues transactions.
  *
  * @t: Pointer to wait_timer in a qh.
+ *
+ * Return: HRTIMER_NORESTART to not automatically restart this timer.
  */
-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 +1493,7 @@ static void dwc2_wait_timer_fn(struct timer_list *t)
 	}
 
 	spin_unlock_irqrestore(&hsotg->lock, flags);
+	return HRTIMER_NORESTART;
 }
 
 /**
@@ -1521,7 +1524,8 @@ 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 +1694,7 @@ 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 +1720,7 @@ 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 +1739,8 @@ 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);