Hi Ricardo,
Thank you for the patch.
On Fri, Dec 13, 2024 at 11:21:02AM +0000, Ricardo Ribalda wrote:
> To implement VIDIOC_QUERYCTRL, we need to read from the hardware all the
> values that were not cached previously. If that read fails, we used to
> report back the error to the user.
>
> Unfortunately this does not play nice with userspace. When they are
> enumerating the contols, the only expect an error when there are no
> "next" control.
>
> This is probably a corner case, and could be handled in userspace, but
> both v4l2-ctl and yavta fail to enumerate all the controls if we return
> then -EIO during VIDIOC_QUERYCTRL. I suspect that there are tons of
> userspace apps handling this wrongly as well.
>
> This patch get around this issue by ignoring the hardware errors and
> always returning 0 if a control exists.
>
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> 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.
Was it transient and random errors, or does the device always fail for
those controls ?
> This could be solved in userspace.. but I suspect that a lot of people
> has copied the implementation of v4l-utils or yavta.
>
> What do you think of this workaround?
Pretending that the control could be queried is problematic. We'll
return invalid values to the user, I don't think that's a good idea. If
the problematic device always returns error for focus controls, we could
add a quirk, and extend the uvc_device_info structure to list the
controls to ignore.
Another option would be to skip over controls that return -EIO within
the kernel, and mark those controls are broken. I think this could be
done transparently for userspace, the first time we try to populate the
cache for such controls, a -EIO error would mark the control as broken,
and from a userspace point of view it wouldn't be visible through as
ioctl.
> 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
>
> --
> ---
> drivers/media/usb/uvc/uvc_ctrl.c | 31 ++++++++++++++++++++++---------
> 1 file changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 4fe26e82e3d1..a11048c9a105 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1283,7 +1283,8 @@ static u32 uvc_get_ctrl_bitmap(struct uvc_control *ctrl,
> static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> struct uvc_control *ctrl,
> struct uvc_control_mapping *mapping,
> - struct v4l2_queryctrl *v4l2_ctrl)
> + struct v4l2_queryctrl *v4l2_ctrl,
> + bool can_fail)
> {
> struct uvc_control_mapping *master_map = NULL;
> struct uvc_control *master_ctrl = NULL;
> @@ -1307,17 +1308,28 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> if (master_ctrl && (master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR)) {
> s32 val;
> int ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
> - if (ret < 0)
> - return ret;
>
> - if (val != mapping->master_manual)
> - v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
> + if (ret < 0) {
> + dev_warn_ratelimited(&chain->dev->udev->dev,
> + "UVC non compliance: Error %d querying master control %x\n",
> + ret, master_map->id);
> + if (can_fail)
> + return ret;
> + } 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;
> +
> + if (ret < 0) {
> + dev_warn_ratelimited(&chain->dev->udev->dev,
> + "UVC non compliance: Error %d populating cache of control %x\n",
> + ret, mapping->id);
> + if (can_fail)
> + return ret;
> + }
> }
>
> if (ctrl->info.flags & UVC_CTRL_FLAG_GET_DEF) {
> @@ -1420,7 +1432,8 @@ int uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> goto done;
> }
>
> - ret = __uvc_query_v4l2_ctrl(chain, ctrl, mapping, v4l2_ctrl);
> + ret = __uvc_query_v4l2_ctrl(chain, ctrl, mapping, v4l2_ctrl,
> + !(v4l2_ctrl->id & V4L2_CTRL_FLAG_NEXT_CTRL));
> done:
> mutex_unlock(&chain->ctrl_mutex);
> return ret;
> @@ -1513,7 +1526,7 @@ static void uvc_ctrl_fill_event(struct uvc_video_chain *chain,
> {
> struct v4l2_queryctrl v4l2_ctrl;
>
> - __uvc_query_v4l2_ctrl(chain, ctrl, mapping, &v4l2_ctrl);
> + __uvc_query_v4l2_ctrl(chain, ctrl, mapping, &v4l2_ctrl, true);
>
> memset(ev, 0, sizeof(*ev));
> ev->type = V4L2_EVENT_CTRL;
>
> ---
> base-commit: a7f5b36b34824415c28875d615c49a3cf5070615
> change-id: 20241213-uvc-eaccess-755cc061a360
--
Regards,
Laurent Pinchart
