Linux-libre 4.4-gnupck-4.4-gnu

1 files changed, 16 insertions, 6 deletions

diff --git a/drivers/usb/musb/musb_host.c b/drivers/usb/musb/musb_host.c
index 26c65e66c..795a45b1b 100644
--- a/drivers/usb/musb/musb_host.c
+++ b/drivers/usb/musb/musb_host.c
@@ -112,22 +112,32 @@ static void musb_h_tx_flush_fifo(struct musb_hw_ep *ep)
 	struct musb	*musb = ep->musb;
 	void __iomem	*epio = ep->regs;
 	u16		csr;
-	u16		lastcsr = 0;
 	int		retries = 1000;
 
 	csr = musb_readw(epio, MUSB_TXCSR);
 	while (csr & MUSB_TXCSR_FIFONOTEMPTY) {
-		if (csr != lastcsr)
-			dev_dbg(musb->controller, "Host TX FIFONOTEMPTY csr: %02x\n", csr);
-		lastcsr = csr;
 		csr |= MUSB_TXCSR_FLUSHFIFO | MUSB_TXCSR_TXPKTRDY;
 		musb_writew(epio, MUSB_TXCSR, csr);
 		csr = musb_readw(epio, MUSB_TXCSR);
-		if (WARN(retries-- < 1,
+
+		/*
+		 * FIXME: sometimes the tx fifo flush failed, it has been
+		 * observed during device disconnect on AM335x.
+		 *
+		 * To reproduce the issue, ensure tx urb(s) are queued when
+		 * unplug the usb device which is connected to AM335x usb
+		 * host port.
+		 *
+		 * I found using a usb-ethernet device and running iperf
+		 * (client on AM335x) has very high chance to trigger it.
+		 *
+		 * Better to turn on dev_dbg() in musb_cleanup_urb() with
+		 * CPPI enabled to see the issue when aborting the tx channel.
+		 */
+		if (dev_WARN_ONCE(musb->controller, retries-- < 1,
 				"Could not flush host TX%d fifo: csr: %04x\n",
 				ep->epnum, csr))
 			return;
-		mdelay(1);
 	}
 }