[PATCH] Coping with short replies in usbmixer

[PATCH] Coping with short replies in usbmixer

[thomas]

[-- Attachment #1: Type: text/plain, Size: 912 bytes --]

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

[-- Attachment #2: usbmixer.patch --]
[-- Type: text/x-patch, Size: 556 bytes --]

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;
 		}

[-- Attachment #3: Type: text/plain, Size: 160 bytes --]

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Re: [PATCH] Coping with short replies in usbmixer

[Takashi Iwai]

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;
>  		}
> [3  <text/plain; us-ascii (7bit)>]
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> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Re: [PATCH] Coping with short replies in usbmixer

[Thomas Reitmayr]

Hi,
here is it again and signed off.

This patch makes sure that short USB replies are treated as an
error when requesting the value of a certain mixer control.

Signed-off-by: Thomas Reitmayr <thomas@devbase.at>
---

 sound/usb/usbmixer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


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;
 		}

Re: [PATCH] Coping with short replies in usbmixer

[Takashi Iwai]

At Mon, 14 May 2007 19:54:34 +0200,
Thomas Reitmayr wrote:
> 
> Hi,
> here is it again and signed off.
> 
> This patch makes sure that short USB replies are treated as an
> error when requesting the value of a certain mixer control.
> 
> Signed-off-by: Thomas Reitmayr <thomas@devbase.at>

Thanks, now applied to ALSA tree.


Takashi