Coping with short replies in usbmixer

PATCH In review [email protected] 2 participants 2 messages May 11, 2007 – May 14, 2007 Sound

Share & tools

[email protected]

author

2007-05-11 20:28 UTC #0 lore raw

PATCH 1/1 Coping with short replies in usbmixer

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

sound/usb/usbmixer.c +1 -1

diff -rup a/sound/usb/usbmixer.c b/sound/usb/usbmixer.c
@@ -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;
 		}

_______________________________________________
Alsa-devel mailing list
[email protected]
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Takashi Iwai

2007-05-14 09:10 UTC #1 lore raw

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

Quoted 14 lines · [email protected] 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.

Quoted 6 lines

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

Quoted 18 lines

[2 usbmixer.patch <text/x-patch (7bit)>]
diff -rup a/sound/usb/usbmixer.c b/sound/usb/usbmixer.c
sound/usb/usbmixer.c +1 -1
@@ -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)>]
_______________________________________________
Alsa-devel mailing list
[email protected]
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel