linux-kernel - Re: [PATCH v2 2/2] media: uvcvideo: Add more logging to uvc_query

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Message-ID: <4ce7cac7-6e4a-45b8-8d0e-a8f16a77839f@redhat.com>
Date: Mon, 18 Nov 2024 17:45:18 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v2 2/2] media: uvcvideo: Add more logging to
 uvc_query_ctrl()

Hi Ricardo,

Thank you for your patch.

On 8-Oct-24 5:00 PM, Ricardo Ribalda wrote:
> If we fail to query the ctrl error code there is no information on dmesg
> or in uvc_dbg. This makes difficult to debug the issue.
> 
> Print a proper error message when we cannot retrieve the error code from
> the device.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_video.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index f125b3ba50f2..6efbfa609059 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -111,8 +111,12 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
>  	error = *(u8 *)data;
>  	*(u8 *)data = tmp;
>  
> -	if (ret != 1)
> -		return ret < 0 ? ret : -EPIPE;
> +	if (ret != 1) {
> +		dev_err(&dev->udev->dev,
> +			"Failed to query (%s) UVC error code control %u on unit %u: %d (exp. 1).\n",
> +			uvc_query_name(query), cs, unit, ret);
> +		return ret ? ret : -EPIPE;

Adding error logging is always good, but again please drop the change
to the return condition and stick with the:

	return ret < 0 ? ret : -EPIPE;

pattern used everywhere.

Also in this case the return condition change really should have
been in a separate patch since unlike before the success condition
did not change, so it really is unrelated to adding the error
logging.

Regards,

Hans