On Monday 29 June 2009, Alan Stern wrote:
> 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@xxxxxxxxxxxxxxxxxxx>
> CC: David Brownell <david-b@xxxxxxxxxxx>
Acked-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
>
> ---
>
> 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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