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649c033711
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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.