[PATCH] usb: gadget: musb: fix short isoc packets with inventra dma for pandaboard es

[Paul Elder <paul.elder@ideasonboard.com>]

Handling short packets (length < max packet size) in the Inventra DMA
engine in the MUSB driver causes the MUSB DMA controller to hang. An
example of a problem that is caused by this problem is when streaming
video out of a UVC gadget, only the first video frame is transferred.

For short packets (mode-0 or mode-1 DMA), MUSB_TXCSR_TXPKTRDY must be
set manually by the driver. This was previously done in musb_g_tx
(musb_gadget.c), but incorrectly (all csr flags were cleared, and only
MUSB_TXCSR_MODE and MUSB_TXCSR_TXPKTRDY). Fixing that problem allows
some requests to be transferred correctly, but multiple requests were
often put together in one USB packet, and caused problems if the packet
size was not a multiple of 4.

Instead, MUSB_TXCSR_TXPKTRDY is set in dma_controller_irq (musbhsdma.c),
just like host mode transfers, then musb_g_tx forces the packet to be
flushed, by setting MUSB_TXCSR_FLUSHFIFO.

This topic was originally tackled by Nicolas Boichat [0] [1] and is discussed
further at [2] as part of his GSoC project [3].

[0] https://groups.google.com/forum/?hl=en#!topic/beagleboard-gsoc/k8Azwfp75CU
[1] https://gitorious.org/beagleboard-usbsniffer/beagleboard-usbsniffer-kernel/commit/b0be3b6cc195ba732189b04f1d43ec843c3e54c9?p=beagleboard-usbsniffer:beagleboard-usbsniffer-kernel.git;a=patch;h=b0be3b6cc195ba732189b04f1d43ec843c3e54c9
[2] http://beagleboard-usbsniffer.blogspot.com/2010/07/musb-isochronous-transfers-fixed.html
[3] http://elinux.org/BeagleBoard/GSoC/USBSniffer

I have forward-ported this patch from 2.6.34 to 4.19-rc1.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
---
 drivers/usb/musb/musb_gadget.c | 21 ++++++++++++++-------
 drivers/usb/musb/musbhsdma.c   | 21 +++++++++++----------
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/usb/musb/musb_gadget.c b/drivers/usb/musb/musb_gadget.c
index eae8b1b1b45b..d3f33f449445 100644
--- a/drivers/usb/musb/musb_gadget.c
+++ b/drivers/usb/musb/musb_gadget.c
@@ -479,11 +479,16 @@ void musb_g_tx(struct musb *musb, u8 epnum)
 			&& (request->actual == request->length))
 				short_packet = true;
 
-		if ((musb_dma_inventra(musb) || musb_dma_ux500(musb)) &&
-			(is_dma && (!dma->desired_mode ||
-				(request->actual &
-					(musb_ep->packet_sz - 1)))))
-				short_packet = true;
+		if (is_dma && (musb_dma_inventra(musb) || musb_dma_ux500(musb))) {
+			if (!dma->desired_mode ||
+					request->actual % musb_ep->packet_sz) {
+				musb_dbg(musb, "%s Flushing (FIFO) EP : KPB\n",
+						musb_ep->end_point.name);
+				musb_writew(epio, MUSB_TXCSR,
+						csr | MUSB_TXCSR_FLUSHFIFO);
+				return;
+			}
+		}
 
 		if (short_packet) {
 			/*
@@ -493,8 +498,10 @@ void musb_g_tx(struct musb *musb, u8 epnum)
 			if (csr & MUSB_TXCSR_TXPKTRDY)
 				return;
 
-			musb_writew(epio, MUSB_TXCSR, MUSB_TXCSR_MODE
-					| MUSB_TXCSR_TXPKTRDY);
+			musb_dbg(musb, "sending zero pkt (zero=%d, length=%d, actual=%d, dma->desired_mode=%d)\n",
+				 request->zero, request->length, request->actual,
+				 dma->desired_mode);
+			musb_writew(epio, MUSB_TXCSR, csr | MUSB_TXCSR_TXPKTRDY);
 			request->zero = 0;
 		}
 
diff --git a/drivers/usb/musb/musbhsdma.c b/drivers/usb/musb/musbhsdma.c
index a688f7f87829..e514d4700a6b 100644
--- a/drivers/usb/musb/musbhsdma.c
+++ b/drivers/usb/musb/musbhsdma.c
@@ -346,12 +346,10 @@ static irqreturn_t dma_controller_irq(int irq, void *private_data)
 				channel->status = MUSB_DMA_STATUS_FREE;
 
 				/* completed */
-				if ((devctl & MUSB_DEVCTL_HM)
-					&& (musb_channel->transmit)
-					&& ((channel->desired_mode == 0)
-					    || (channel->actual_len &
-					    (musb_channel->max_packet_sz - 1)))
-				    ) {
+				if (musb_channel->transmit &&
+				    (!channel->desired_mode ||
+				     (channel->actual_len %
+				      musb_channel->max_packet_sz))) {
 					u8  epnum  = musb_channel->epnum;
 					int offset = musb->io.ep_offset(epnum,
 								    MUSB_TXCSR);
@@ -363,11 +361,14 @@ static irqreturn_t dma_controller_irq(int irq, void *private_data)
 					 */
 					musb_ep_select(mbase, epnum);
 					txcsr = musb_readw(mbase, offset);
-					txcsr &= ~(MUSB_TXCSR_DMAENAB
+					if (channel->desired_mode == 1) {
+						txcsr &= ~(MUSB_TXCSR_DMAENAB
 							| MUSB_TXCSR_AUTOSET);
-					musb_writew(mbase, offset, txcsr);
-					/* Send out the packet */
-					txcsr &= ~MUSB_TXCSR_DMAMODE;
+						musb_writew(mbase, offset, txcsr);
+						/* Send out the packet */
+						txcsr &= ~MUSB_TXCSR_DMAMODE;
+						txcsr |= MUSB_TXCSR_DMAENAB;
+					}
 					txcsr |=  MUSB_TXCSR_TXPKTRDY;
 					musb_writew(mbase, offset, txcsr);
 				}
-- 
2.18.0