At Fri, 11 May 2007 22:28:16 +0200,
thomas@xxxxxxxxxx wrote:
>
> Hi,
> while trying to find out why a USB handset (Yealink P1K) frequently gets
> muted when changing volume, I found that short USB responses cause the
> problem.
>
> The function get_ctl_value(..) in usbmixer.c requests the state of a
> certain control and retries up to 10 times if an error occurs. However a
> short USB response is not treated as an error as neither the transfer
> flag URB_SHORT_NOT_OK is set nor is the return value of
> snd_usb_ctl_msg(..) compared with the requested amount of data. As a
> result the function get_ctl_value(..) might not retry the USB request
> but returns an unpredictable result without reporting an error.
>
> The attached patch forces the number of returned bytes to be at least
> val_len. It was generated from kernel version 2.6.21. If there are any
> issues with the patch please let me know. Otherwise I would be happy if
> it could be applied to the ALSA sources.
> Regards,
> -Thomas
Thanks, the patch looks good.
Could you give a sign-off to merge to the upstream?
Takashi
> [2 usbmixer.patch <text/x-patch (7bit)>]
> diff -rup a/sound/usb/usbmixer.c b/sound/usb/usbmixer.c
> --- a/sound/usb/usbmixer.c 2007-05-11 21:58:33.000000000 +0200
> +++ b/sound/usb/usbmixer.c 2007-05-11 21:59:14.000000000 +0200
> @@ -360,7 +360,7 @@ static int get_ctl_value(struct usb_mixe
> request,
> USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
> validx, cval->mixer->ctrlif | (cval->id << 8),
> - buf, val_len, 100) >= 0) {
> + buf, val_len, 100) >= val_len) {
> *value_ret = convert_signed_value(cval, snd_usb_combine_bytes(buf, val_len));
> return 0;
> }
> [3 <text/plain; us-ascii (7bit)>]
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