Hi Ricardo,
Thank you for the patch.
On Mon, Aug 18, 2025 at 08:15:38PM +0000, 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.
Looking at the commit that introduced this code
commit 52c58ad6f95ff60343bf0c517182d5f649ca0403
Author: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Date: Wed Sep 29 16:03:03 2010 -0300
[media] uvcvideo: Delay initialization of XU controls
we see it contains the following change
- /* Query XU controls for control information */
- if (UVC_ENTITY_TYPE(ctrl->entity) == UVC_VC_EXTENSION_UNIT) {
- struct uvc_control_info info;
- int ret;
-
- ret = uvc_ctrl_fill_xu_info(dev, ctrl, &info);
- if (ret < 0)
- return;
-
- ret = uvc_ctrl_add_info(dev, ctrl, &info);
- if (ret < 0) {
- /* Skip the control */
- uvc_trace(UVC_TRACE_CONTROL, "Failed to initialize "
- "control %pUl/%u on device %s entity %u\n",
- info.entity, info.selector, dev->udev->devpath,
- ctrl->entity->id);
- memset(ctrl, 0, sizeof(*ctrl));
- }
+ /* 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;
- }
This is followed by
for (; info < iend; ++info) {
if (uvc_entity_match_guid(ctrl->entity, info->entity) &&
ctrl->index == info->index) {
uvc_ctrl_add_info(dev, ctrl, info);
break;
}
}
if (!ctrl->initialized)
return;
(this loops over uvc_ctrls). As uvc_ctrls doesn't contain any non-XU
control, you're right that the function never calls uvc_ctrl_add_info()
for XU controls. The ctrl->initialized check then causes the function to
return, as uvc_ctrl_add_info() wasn't called and initialized is false.
The entity type check was therefore not needed, and can be removed.
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxx>
> ---
> 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];
>
--
Regards,
Laurent Pinchart
