linux-kernel - Re: [PATCH v7 2/8] media: uvcvideo: Add support for per-device control mapping overrides

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Date:   Fri, 17 Jun 2022 16:44:02 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        tfiga@...omium.org, senozhatsky@...omium.org, yunkec@...gle.com
Subject: Re: [PATCH v7 2/8] media: uvcvideo: Add support for per-device
 control mapping overrides

Hi Ricardo,

Thank you for the patch.

On Fri, Jun 17, 2022 at 12:36:39PM +0200, Ricardo Ribalda wrote:
> Some devices do not implement all their controls in a way that complies
> with the UVC specification. This is for instance the case for several
> devices that do not support the disabled mode for the power line
> frequency control. Add a mechanism to allow per-device control mapping
> overrides to avoid errors when accessing non-compliant controls.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 35 ++++++++++++++++++++++++++------
>  drivers/media/usb/uvc/uvcvideo.h |  1 +
>  2 files changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index a709ebbb4d69..092decfdaa62 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -2403,9 +2403,8 @@ static void uvc_ctrl_init_ctrl(struct uvc_video_chain *chain,
>  {
>  	const struct uvc_control_info *info = uvc_ctrls;
>  	const struct uvc_control_info *iend = info + ARRAY_SIZE(uvc_ctrls);
> -	const struct uvc_control_mapping *mapping = uvc_ctrl_mappings;
> -	const struct uvc_control_mapping *mend =
> -		mapping + ARRAY_SIZE(uvc_ctrl_mappings);
> +	const struct uvc_control_mapping *mapping;
> +	const struct uvc_control_mapping *mend;
>  
>  	/* XU controls initialization requires querying the device for control
>  	 * information. As some buggy UVC devices will crash when queried
> @@ -2433,14 +2432,38 @@ static void uvc_ctrl_init_ctrl(struct uvc_video_chain *chain,
>  	if (!ctrl->initialized)
>  		return;
>  
> -	/* Process common mappings first. */
> -	for (; mapping < mend; ++mapping) {
> +	/*
> +	 * First check if the device provides a custom mapping for this control,
> +	 * used to override standard mappings for non-conformant devices. Don't
> +	 * process standard mappings if a custom mapping is found. This
> +	 * mechanism doesn't support combining standard and custom mappings for
> +	 * a single control.
> +	 */
> +	if (chain->dev->info->mappings) {
> +		bool custom = false;
> +		unsigned int i;
> +
> +		for (i = 0; (mapping = chain->dev->info->mappings[i]); ++i) {
> +			if (uvc_entity_match_guid(ctrl->entity, mapping->entity) &&
> +			    ctrl->info.selector == mapping->selector) {
> +				__uvc_ctrl_add_mapping(chain, ctrl, mapping);
> +				custom = true;
> +			}
> +		}
> +
> +		if (custom)
> +			return;
> +	}
> +
> +	/* Process common mappings next. */
> +	mend = mapping + ARRAY_SIZE(uvc_ctrl_mappings);

I don't think mapping has the right value here, it could even be
uninitialized. Let's make this

	mapping = uvc_ctrl_mappings;
	mend = mapping + ARRAY_SIZE(uvc_ctrl_mappings);

	for (; mapping < mend; ++mapping) {

to match the code below.

> +	for (mapping = uvc_ctrl_mappings; mapping < mend; ++mapping) {
>  		if (uvc_entity_match_guid(ctrl->entity, mapping->entity) &&
>  		    ctrl->info.selector == mapping->selector)
>  			__uvc_ctrl_add_mapping(chain, ctrl, mapping);
>  	}
>  
> -	/* And then version-specific mappings. */
> +	/* Finally process version-specific mappings. */
>  	if (chain->dev->uvc_version < 0x0150) {
>  		mapping = uvc_ctrl_mappings_uvc11;
>  		mend = mapping + ARRAY_SIZE(uvc_ctrl_mappings_uvc11);
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index c5b4febd2d94..fff5c5c99a3d 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -667,6 +667,7 @@ struct uvc_device_info {
>  	u32	quirks;
>  	u32	meta_format;
>  	u16	uvc_version;
> +	const struct uvc_control_mapping **mappings;
>  };
>  
>  struct uvc_device {

-- 
Regards,

Laurent Pinchart