media: uvcvideo: Set V4L2_CTRL_FLAG_DISABLED during queryctrl errors

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 for -EIO errors.
- Introduces a warning in dmesg so we can have a trace of what has happened
  and sets the V4L2_CTRL_FLAG_DISABLED.
- Makes sure we keep returning V4L2_CTRL_FLAG_DISABLED for all the next
  attempts to query that control (other operations have the same
  functionality as now).

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Link: https://lore.kernel.org/r/20250502-uvc-eaccess-v8-1-0b8b58ac1142@chromium.org
Signed-off-by: Hans de Goede <hansg@kernel.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

0 files changed, 0 insertions, 0 deletions