media: v4l2-ctrls: add support for V4L2_CTRL_WHICH_MIN/MAX_VAL

Add the capability of retrieving the min and max values of a
compound control.

[Ricardo: Added static to v4l2_ctrl_type_op_(maximum|minimum) proto]
[Ricardo: Fix documentation]

Signed-off-by: Yunke Cao <yunkec@google.com>
Tested-by: Yunke Cao <yunkec@google.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Link: https://lore.kernel.org/r/20250203-uvc-roi-v17-2-5900a9fed613@chromium.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
[hverkuil: fix small alignment checkpatch warning]

2 files changed, 25 insertions, 6 deletions

diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
index b74a74ac06fc..b8698b85bd80 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
@@ -338,14 +338,26 @@ still cause this situation.
       - Which value of the control to get/set/try.
     * - :cspan:`2` ``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of
 	the control, ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
-	value of the control and ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
-	these controls have to be retrieved from a request or tried/set for
-	a request. In the latter case the ``request_fd`` field contains the
+	value of the control, ``V4L2_CTRL_WHICH_MIN_VAL`` will return the minimum
+	value of the control, and ``V4L2_CTRL_WHICH_MAX_VAL`` will return the maximum
+	value of the control. ``V4L2_CTRL_WHICH_REQUEST_VAL`` indicates that
+	the control value has to be retrieved from a request or tried/set for
+	a request. In that case the ``request_fd`` field contains the
 	file descriptor of the request that should be used. If the device
 	does not support requests, then ``EACCES`` will be returned.
 
-	When using ``V4L2_CTRL_WHICH_DEF_VAL`` be aware that you can only
-	get the default value of the control, you cannot set or try it.
+	When using ``V4L2_CTRL_WHICH_DEF_VAL``, ``V4L2_CTRL_WHICH_MIN_VAL``
+	or ``V4L2_CTRL_WHICH_MAX_VAL`` be aware that you can only get the
+	default/minimum/maximum value of the control, you cannot set or try it.
+
+	Whether a control supports querying the minimum and maximum values using
+	``V4L2_CTRL_WHICH_MIN_VAL`` and ``V4L2_CTRL_WHICH_MAX_VAL`` is indicated
+	by the ``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX`` flag. Most non-compound
+	control types support this. For controls with compound types, the
+	definition of minimum/maximum values are provided by
+	the control documentation. If a compound control does not document the
+	meaning of minimum/maximum value, then querying the minimum or maximum
+	value will result in the error code -EINVAL.
 
 	For backwards compatibility you can also use a control class here
 	(see :ref:`ctrl-class`). In that case all controls have to
diff --git a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
index 56d5c8b0b88b..3549417c7feb 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-queryctrl.rst
@@ -447,7 +447,10 @@ See also the examples in :ref:`control`.
       - n/a
       - A struct :c:type:`v4l2_rect`, containing a rectangle described by
 	the position of its top-left corner, the width and the height. Units
-	depend on the use case.
+	depend on the use case. Support for ``V4L2_CTRL_WHICH_MIN_VAL`` and
+	``V4L2_CTRL_WHICH_MAX_VAL`` is optional and depends on the
+	``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX`` flag. See the documentation of
+	the specific control on how to interpret the minimum and maximum values.
     * - ``V4L2_CTRL_TYPE_H264_SPS``
       - n/a
       - n/a
@@ -664,6 +667,10 @@ See also the examples in :ref:`control`.
 	``dims[0]``. So setting the control with a differently sized
 	array will change the ``elems`` field when the control is
 	queried afterwards.
+    * - ``V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX``
+      - 0x1000
+      - This control supports getting minimum and maximum values using
+        vidioc_g_ext_ctrls with V4L2_CTRL_WHICH_MIN/MAX_VAL.
 
 Return Value
 ============