Re: [PATCH v5] media: uvcvideo: Set V4L2_CTRL_FLAG_DISABLED during queryctrl errors

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, Feb 24, 2025 at 09:40:06AM +0000, Ricardo Ribalda wrote:
> To implement VIDIOC_QUERYCTRL, we need to know the minimum, maximum,
> step and flags of the control. For some of the controls, this involves
> querying the actual hardware.
> 
> Some non-compliant cameras produce errors when we query them. These
> error can be triggered every time, sometimes, or when other controls do
> not have the "right value". Right now, we populate that error to userspace.
> When an error happens, the v4l2 framework does not copy the v4l2_queryctrl
> struct to userspace. Also, userspace apps are not ready to handle any
> other error than -EINVAL.
> 
> One of the main usecases of VIDIOC_QUERYCTRL is enumerating the controls
> of a device. This is done using the V4L2_CTRL_FLAG_NEXT_CTRL flag. In
> that usecase, a non-compliant control will make it almost impossible to
> enumerate all controls of the device.
> 
> A control with an invalid max/min/step/flags is better than non being
> able to enumerate the rest of the controls.
> 
> This patch:
> - Retries for an extra attempt to read the control, to avoid spurious
>   errors. More attempts do not seem to produce better results in the
>   tested hardware.
> - Makes VIDIOC_QUERYCTRL return 0 in all the error cases different than
>   -EINVAL.
> - Introduces a warning in dmesg so we can have a trace of what has happened
>   and sets the V4L2_CTRL_FLAG_DISABLED.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
> Hi 2*Hans and Laurent!
> 
> I came around a device that was listing just a couple of controls when
> it should be listing much more.
> 
> Some debugging latter I found that the device was returning -EIO when
> all the focal controls were read.
> 
> Lots of good arguments in favor/against this patch in the v1. Please
> check!

Let's continue the discussion on v4.

> Without this patch:
> $ v4l2-ctl --list-ctrls
>                   auto_exposure 0x009a0901 (menu)   : min=0 max=3 default=3 value=3 (Aperture Priority Mode)
>          exposure_time_absolute 0x009a0902 (int)    : min=50 max=10000 step=1 default=166 value=166 flags=inactive
>      exposure_dynamic_framerate 0x009a0903 (bool)   : default=0 value=0
> region_of_interest_auto_control 0x009a1902 (bitmask): max=0x00000001 default=0x00000001 value=1
> 
> With this patch:
> $ v4l2-ctl --list-ctrls
>                   auto_exposure 0x009a0901 (menu)   : min=0 max=3 default=3 value=3 (Aperture Priority Mode)
>          exposure_time_absolute 0x009a0902 (int)    : min=50 max=10000 step=1 default=166 value=166 flags=inactive
>      exposure_dynamic_framerate 0x009a0903 (bool)   : default=0 value=0
> error 5 getting ext_ctrl Focus, Absolute
> error 5 getting ext_ctrl Focus, Automatic Continuous
>    region_of_interest_rectangle 0x009a1901 (unknown): type=107 value=unsupported payload type flags=has-payload
> region_of_interest_auto_control 0x009a1902 (bitmask): max=0x00000001 default=0x00000001 value=1
> --
> ---
> Changes in v5:
> - Explain the retry in the commit message (Thanks Laurent).
> - Link to v4: https://lore.kernel.org/r/20250111-uvc-eaccess-v4-1-c7759bfd1bd4@chromium.org
> 
> Changes in v4:
> - Display control name (Thanks Hans)
> - Link to v3: https://lore.kernel.org/r/20250107-uvc-eaccess-v3-1-99f3335d5133@chromium.org
> 
> Changes in v3:
> - Add a retry mechanism during error.
> - Set V4L2_CTRL_FLAG_DISABLED flag.
> - Link to v2: https://lore.kernel.org/r/20241219-uvc-eaccess-v2-1-bf6520c8b86d@chromium.org
> 
> Changes in v2:
> - Never return error, even if we are not enumerating the controls
> - Improve commit message.
> - Link to v1: https://lore.kernel.org/r/20241213-uvc-eaccess-v1-1-62e0b4fcc634@chromium.org
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 43 ++++++++++++++++++++++++++++++++--------
>  1 file changed, 35 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 4e58476d305e..9d7812e8572d 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1280,6 +1280,8 @@ static u32 uvc_get_ctrl_bitmap(struct uvc_control *ctrl,
>  	return ~0;
>  }
>  
> +#define MAX_QUERY_RETRIES 2
> +
>  static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
>  	struct uvc_control *ctrl,
>  	struct uvc_control_mapping *mapping,
> @@ -1305,19 +1307,44 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
>  		__uvc_find_control(ctrl->entity, mapping->master_id,
>  				   &master_map, &master_ctrl, 0);
>  	if (master_ctrl && (master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR)) {
> +		unsigned int retries;
>  		s32 val;
> -		int ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
> -		if (ret < 0)
> -			return ret;
> +		int ret;
>  
> -		if (val != mapping->master_manual)
> -				v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
> +		for (retries = 0; retries < MAX_QUERY_RETRIES; retries++) {
> +			ret = __uvc_ctrl_get(chain, master_ctrl, master_map,
> +					     &val);
> +			if (ret >= 0)
> +				break;
> +		}
> +
> +		if (ret < 0) {
> +			dev_warn_ratelimited(&chain->dev->udev->dev,
> +					     "UVC non compliance: Error %d querying master control %x (%s)\n",
> +					      ret, master_map->id,
> +					      uvc_map_get_name(master_map));
> +		} else if (val != mapping->master_manual) {
> +			v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
> +		}
>  	}
>  
>  	if (!ctrl->cached) {
> -		int ret = uvc_ctrl_populate_cache(chain, ctrl);
> -		if (ret < 0)
> -			return ret;
> +		unsigned int retries;
> +		int ret;
> +
> +		for (retries = 0; retries < MAX_QUERY_RETRIES; retries++) {
> +			ret = uvc_ctrl_populate_cache(chain, ctrl);
> +			if (ret >= 0)
> +				break;
> +		}
> +
> +		if (ret < 0) {
> +			dev_warn_ratelimited(&chain->dev->udev->dev,
> +					     "UVC non compliance: Error %d populating cache of control %x (%s)\n",
> +					     ret, mapping->id,
> +					     uvc_map_get_name(mapping));
> +			v4l2_ctrl->flags |= V4L2_CTRL_FLAG_DISABLED;
> +		}
>  	}
>  
>  	if (ctrl->info.flags & UVC_CTRL_FLAG_GET_DEF) {
> 
> ---
> base-commit: c2b96a6818159fba8a3bcc38262da9e77f9b3ec7
> change-id: 20241213-uvc-eaccess-755cc061a360
> 
> Best regards,
> -- 
> Ricardo Ribalda <ribalda@chromium.org>
> 

-- 
Regards,

Laurent Pinchart