linux-kernel - Re: [PATCH 3/4] media: uvcvideo: Run uvc_ctrl_init

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Message-ID: <e3aa47fe-938b-43f1-b221-02e3e4c74243@kernel.org>
Date: Mon, 8 Sep 2025 13:02:32 +0200
From: Hans de Goede <hansg@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Hans Verkuil <hverkuil@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org
Subject: Re: [PATCH 3/4] media: uvcvideo: Run uvc_ctrl_init_ctrl for all
 controls

Hi,

On 18-Aug-25 22:15, Ricardo Ribalda wrote:
> The function uvc_ctrl_init_ctrl() is called for every control for every
> entity, but it exits early if the entity is a extension unit. The comment
> claims that this is done to avoid querying XU controls during probe.
> 
> We only query a control if its entity GUIDs and index matches the
> uvc_ctrls list. There are only controls for the following GUIDs:
> UVC_GUID_UVC_PROCESSING, UVC_GUID_UVC_CAMERA and
> UVC_GUID_EXT_GPIO_CONTROLLER.
> 
> In other words, XU controls will not be queried even without this
> condition.
> 
> In future patches we want to add ChromeOS XU controls that need to the
> initialized. We will make sure that all cameras with ChromeOS XU can
> be queried at probe time.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <hansg@...nel.org>

Regards,

Hans



> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index efe609d7087752cb2ef516eef0fce12acd13e747..ff975f96e1325532e2299047c07de5d1b9cf09db 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -3181,15 +3181,6 @@ static void uvc_ctrl_init_ctrl(struct uvc_video_chain *chain,
>  {
>  	unsigned int i;
>  
> -	/*
> -	 * XU controls initialization requires querying the device for control
> -	 * information. As some buggy UVC devices will crash when queried
> -	 * repeatedly in a tight loop, delay XU controls initialization until
> -	 * first use.
> -	 */
> -	if (UVC_ENTITY_TYPE(ctrl->entity) == UVC_VC_EXTENSION_UNIT)
> -		return;
> -
>  	for (i = 0; i < ARRAY_SIZE(uvc_ctrls); ++i) {
>  		const struct uvc_control_info *info = &uvc_ctrls[i];
>  
>