[PATCH v4 2/3] usb: dwc3: gadget: make starting isoc transfers more robust

[Michael Grzeschik <m.grzeschik@pengutronix.de>]

From: Michael Olbrich <m.olbrich@pengutronix.de>

Currently __dwc3_gadget_start_isoc must be called very shortly after
XferNotReady. Otherwise the frame number is outdated and start transfer
will fail, even with several retries.

DSTS provides the lower 14 bit of the frame number. Use it in combination
with the frame number provided by XferNotReady to guess the current frame
number. This will succeed unless more than one 14 rollover has happened
since XferNotReady.

Start transfer might still fail if the frame number is increased
immediately after DSTS is read. So retries are still needed.
Don't drop the current request if this happens. This way it is not lost and
can be used immediately to try again with the next frame number.

With this change, __dwc3_gadget_start_isoc is still not successfully in all
cases bit it increases the acceptable delay after XferNotReady
significantly.

Reviewed-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

---
v1 -> v2: - removed last_frame_number from struct
          - included rollover variable
v2 -> v3: - moved the calculation before the retry loop
          - skipping the calculation if bInterval > 14
v3 -> v4: - used define for 0x3fff framenumber mask
          - added limitation for this to usb > fullspeed

 drivers/usb/dwc3/gadget.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 5fb78535efa9bdc..a2145f905d67067 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1463,6 +1463,7 @@ static int dwc3_gadget_start_isoc_quirk(struct dwc3_ep *dep)
 
 static int __dwc3_gadget_start_isoc(struct dwc3_ep *dep)
 {
+	const struct usb_endpoint_descriptor *desc = dep->endpoint.desc;
 	struct dwc3 *dwc = dep->dwc;
 	int ret;
 	int i;
@@ -1480,6 +1481,27 @@ static int __dwc3_gadget_start_isoc(struct dwc3_ep *dep)
 			return dwc3_gadget_start_isoc_quirk(dep);
 	}
 
+	if (desc->bInterval <= 14 &&
+	    dwc->gadget.speed >= USB_SPEED_SUPER) {
+		u32 frame = __dwc3_gadget_get_frame(dwc);
+		bool rollover = frame <
+				(dep->frame_number & DWC3_FRNUMBER_MASK);
+
+		/*
+		 * frame_number is set from XferNotReady and may be already
+		 * out of date. DSTS only provides the lower 14 bit of the
+		 * current frame number. So add the upper two bits of
+		 * frame_number and handle a possible rollover.
+		 * This will provide the correct frame_number unless more than
+		 * rollover has happened since XferNotReady.
+		 */
+
+		dep->frame_number = (dep->frame_number & ~DWC3_FRNUMBER_MASK) |
+				     frame;
+		if (rollover)
+			dep->frame_number += BIT(14);
+	}
+
 	for (i = 0; i < DWC3_ISOC_MAX_RETRIES; i++) {
 		dep->frame_number = DWC3_ALIGN_FRAME(dep, i + 1);
 
-- 
2.27.0