usb: dwc3: gadget: Correct ISOC DATA PIDs for short packets

The PIDs for Isochronous data transfers are incorrect
for high bandwidth IN endpoints when the request length
is less than EP wMaxPacketSize.

As per spec correct PIDs for ISOC data transfers are:

1) For request length <= maxpacket
	- DATA0,

2) For maxpacket < length <= (2 * maxpacket)
	- DATA1, DATA0

3) For (2 * maxpacket) <  length <= (3 * maxpacket)
	- DATA2, DATA1, DATA0.

But driver always sets PCM fields based on wMaxPacketSize
due to which DATA2 happens even for small requests.

Fix this by setting the PCM field of trb->size depending
on request length rather than fixing it to the value
depending on wMaxPacketSize.

Ideally it shouldn't give any issues as dwc3 will send
0-length packet for next IN token if host sends (even
after receiving a short packet). Windows seems to ignore
this but with MacOS frame loss observed when using f_uvc.
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -896,9 +896,40 @@ static void __dwc3_prepare_one_trb(struct dwc3_ep *dep, struct dwc3_trb *trb,
 		if (!node) {
 			trb->ctrl = DWC3_TRBCTL_ISOCHRONOUS_FIRST;
 
+			/*
+			 * USB Specification 2.0 Section 5.9.2 states that: "If
+			 * there is only a single transaction in the microframe,
+			 * only a DATA0 data packet PID is used.  If there are
+			 * two transactions per microframe, DATA1 is used for
+			 * the first transaction data packet and DATA0 is used
+			 * for the second transaction data packet.  If there are
+			 * three transactions per microframe, DATA2 is used for
+			 * the first transaction data packet, DATA1 is used for
+			 * the second, and DATA0 is used for the third."
+			 *
+			 * IOW, we should satisfy the following cases:
+			 *
+			 * 1) length <= maxpacket
+			 *	- DATA0
+			 *
+			 * 2) maxpacket < length <= (2 * maxpacket)
+			 *	- DATA1, DATA0
+			 *
+			 * 3) (2 * maxpacket) < length <= (3 * maxpacket)
+			 *	- DATA2, DATA1, DATA0
+			 */
 			if (speed == USB_SPEED_HIGH) {
 				struct usb_ep *ep = &dep->endpoint;
-				trb->size |= DWC3_TRB_SIZE_PCM1(ep->mult - 1);
+				unsigned int mult = ep->mult - 1;
+				unsigned int maxp = usb_endpoint_maxp(ep->desc);
+
+				if (length <= (2 * maxp))
+					mult--;
+
+				if (length <= maxp)
+					mult--;
+
+				trb->size |= DWC3_TRB_SIZE_PCM1(mult);
 			}
 		} else {
 			trb->ctrl = DWC3_TRBCTL_ISOCHRONOUS;