usb: musb: fix cppi channel teardown for isoch transfer

commit b431ba88 upstream.

After a few iterations of start/stop UVC camera streaming, the streaming
stops.

This patch adds 250us delay in the cppi channel abort path to let cppi
drain properly.

Using 50us delay seems to be too aggressive, some webcams are still
broken. 250us is the original value used in TI 3.2 kernel.
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Cc: Oliver Neukum <ONeukum@suse.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/usb/musb/musb_cppi41.c

@@ -509,6 +509,9 @@ static int cppi41_dma_channel_abort(struct dma_channel *channel)
 	} else {
 		cppi41_set_autoreq_mode(cppi41_channel, EP_MODE_AUTOREQ_NONE);
 
+		/* delay to drain to cppi dma pipeline for isoch */
+		udelay(250);
+
 		csr = musb_readw(epio, MUSB_RXCSR);
 		csr &= ~(MUSB_RXCSR_H_REQPKT | MUSB_RXCSR_DMAENAB);
 		musb_writew(epio, MUSB_RXCSR, csr);