USB: EHCI: check for STALL before other errors

This patch (as1257) revises the way ehci-hcd detects STALLs.  The
logic is a little peculiar because there's no hardware status bit
specifically meant to indicate a STALL.  You just have to guess that a
STALL was received if the BABBLE bit (which is fatal) isn't set and
the transfer stopped before all its retries were used up.

The existing code doesn't do this properly, because it tests for MMF
(Missed MicroFrame) and DBE (Data Buffer Error) before testing the
retry counter.  Thus, if a transaction gets either MMF or DBE the
corresponding flag is set and the transaction is retried.  If the
second attempt receives a STALL then -EPIPE is the correct return
value.  But the existing code would see the MMF or DBE flag instead
and return -EPROTO, -ENOSR, or -ECOMM.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/ehci-q.c

@@ -214,6 +214,14 @@ static int qtd_copy_status (
 		if (token & QTD_STS_BABBLE) {
 			/* FIXME "must" disable babbling device's port too */
 			status = -EOVERFLOW;
+		/* CERR nonzero + halt --> stall */
+		} else if (QTD_CERR(token)) {
+			status = -EPIPE;
+
+		/* In theory, more than one of the following bits can be set
+		 * since they are sticky and the transaction is retried.
+		 * Which to test first is rather arbitrary.
+		 */
 		} else if (token & QTD_STS_MMF) {
 			/* fs/ls interrupt xfer missed the complete-split */
 			status = -EPROTO;
@@ -222,21 +230,15 @@ static int qtd_copy_status (
 				? -ENOSR  /* hc couldn't read data */
 				: -ECOMM; /* hc couldn't write data */
 		} else if (token & QTD_STS_XACT) {
-			/* timeout, bad crc, wrong PID, etc; retried */
-			if (QTD_CERR (token))
-				status = -EPIPE;
-			else {
-				ehci_dbg (ehci, "devpath %s ep%d%s 3strikes\n",
-					urb->dev->devpath,
-					usb_pipeendpoint (urb->pipe),
-					usb_pipein (urb->pipe) ? "in" : "out");
-				status = -EPROTO;
-			}
-		/* CERR nonzero + no errors + halt --> stall */
-		} else if (QTD_CERR (token))
-			status = -EPIPE;
-		else	/* unknown */
+			/* timeout, bad CRC, wrong PID, etc */
+			ehci_dbg(ehci, "devpath %s ep%d%s 3strikes\n",
+				urb->dev->devpath,
+				usb_pipeendpoint(urb->pipe),
+				usb_pipein(urb->pipe) ? "in" : "out");
+			status = -EPROTO;
+		} else {	/* unknown */
 			status = -EPROTO;
+		}
 
 		ehci_vdbg (ehci,
 			"dev%d ep%d%s qtd token %08x --> status %d\n",