On Monday 29 June 2009, Alan Stern wrote:
quoted text
> 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>
> CC: David Brownell <david-b@pacbell.net>

Acked-by: David Brownell <dbrownell@users.sourceforge.net>

quoted text
> 
> ---
> 
> Index: usb-2.6/drivers/usb/host/ehci-q.c
> ===================================================================
> --- usb-2.6.orig/drivers/usb/host/ehci-q.c
> +++ usb-2.6/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",
> 
> 



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