USB: musb_host, fix ep0 fifo flushing

The MUSB host side can't share generic TX FIFO flush logic
with EP0; the EP0 TX status register bits are different
from those for other entpoints.

Resolve this issue by providing a new EP0-specific routine
to flush and reset the FIFO, which pays careful attention to
restrictions listed in the latest programmer's guide.  This
gets rid of an open issue whereby the usbtest control write
test (#14) failed.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/musb/musb_host.c

@@ -125,6 +125,29 @@ static void musb_h_tx_flush_fifo(struct musb_hw_ep *ep)
 	}
 }
 
+static void musb_h_ep0_flush_fifo(struct musb_hw_ep *ep)
+{
+	void __iomem	*epio = ep->regs;
+	u16		csr;
+	int		retries = 5;
+
+	/* scrub any data left in the fifo */
+	do {
+		csr = musb_readw(epio, MUSB_TXCSR);
+		if (!(csr & (MUSB_CSR0_TXPKTRDY | MUSB_CSR0_RXPKTRDY)))
+			break;
+		musb_writew(epio, MUSB_TXCSR, MUSB_CSR0_FLUSHFIFO);
+		csr = musb_readw(epio, MUSB_TXCSR);
+		udelay(10);
+	} while (--retries);
+
+	WARN(!retries, "Could not flush host TX%d fifo: csr: %04x\n",
+			ep->epnum, csr);
+
+	/* and reset for the next transfer */
+	musb_writew(epio, MUSB_TXCSR, 0);
+}
+
 /*
  * Start transmit. Caller is responsible for locking shared resources.
  * musb must be locked.
@@ -694,10 +717,7 @@ static void musb_ep_program(struct musb *musb, u8 epnum,
 			csr = musb_readw(epio, MUSB_TXCSR);
 		} else {
 			/* endpoint 0: just flush */
-			musb_writew(epio, MUSB_CSR0,
-				csr | MUSB_CSR0_FLUSHFIFO);
-			musb_writew(epio, MUSB_CSR0,
-				csr | MUSB_CSR0_FLUSHFIFO);
+			musb_h_ep0_flush_fifo(hw_ep);
 		}
 
 		/* target addr and (for multipoint) hub addr/port */
@@ -1063,11 +1083,7 @@ irqreturn_t musb_h_ep0_irq(struct musb *musb)
 			csr &= ~MUSB_CSR0_H_NAKTIMEOUT;
 			musb_writew(epio, MUSB_CSR0, csr);
 		} else {
-			csr |= MUSB_CSR0_FLUSHFIFO;
-			musb_writew(epio, MUSB_CSR0, csr);
-			musb_writew(epio, MUSB_CSR0, csr);
-			csr &= ~MUSB_CSR0_H_NAKTIMEOUT;
-			musb_writew(epio, MUSB_CSR0, csr);
+			musb_h_ep0_flush_fifo(hw_ep);
 		}
 
 		musb_writeb(epio, MUSB_NAKLIMIT0, 0);
@@ -1081,10 +1097,7 @@ irqreturn_t musb_h_ep0_irq(struct musb *musb)
 		 * SHOULD NEVER HAPPEN! */
 		ERR("no URB for end 0\n");
 
-		musb_writew(epio, MUSB_CSR0, MUSB_CSR0_FLUSHFIFO);
-		musb_writew(epio, MUSB_CSR0, MUSB_CSR0_FLUSHFIFO);
-		musb_writew(epio, MUSB_CSR0, 0);
-
+		musb_h_ep0_flush_fifo(hw_ep);
 		goto done;
 	}
 
@@ -2043,7 +2056,7 @@ static int musb_cleanup_urb(struct urb *urb, struct musb_qh *qh, int is_in)
 		 * endpoint's irq status here to avoid bogus irqs.
 		 * clearing that status is platform-specific...
 		 */
-	} else {
+	} else if (ep->epnum) {
 		musb_h_tx_flush_fifo(ep);
 		csr = musb_readw(epio, MUSB_TXCSR);
 		csr &= ~(MUSB_TXCSR_AUTOSET
@@ -2057,6 +2070,8 @@ static int musb_cleanup_urb(struct urb *urb, struct musb_qh *qh, int is_in)
 		musb_writew(epio, MUSB_TXCSR, csr);
 		/* flush cpu writebuffer */
 		csr = musb_readw(epio, MUSB_TXCSR);
+	} else  {
+		musb_h_ep0_flush_fifo(ep);
 	}
 	if (status == 0)
 		musb_advance_schedule(ep->musb, urb, ep, is_in);