[alsa-devel] [PATCH] Coping with short replies in usbmixer

[Takashi Iwai]

At Fri, 11 May 2007 22:28:16 +0200,
thomas at devbase.at 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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