At Fri, 11 May 2007 22:28:16 +0200, thomas@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;
  

  }

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