[PATCH v9 17/22] media: docs: Document the behaviour of uvcdriver

From: Ricardo Ribalda
Date: Fri Mar 26 2021 - 06:01:05 EST


The uvc driver relies on the camera firmware to keep the control states
and therefore is not capable of changing an inactive control.

Allow returning -EACESS in those cases.

Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst | 5 +++++
Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst | 5 +++++
2 files changed, 10 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
index 4f1bed53fad5..8c0a203385c2 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
@@ -95,3 +95,8 @@ EBUSY

EACCES
Attempt to set a read-only control or to get a write-only control.
+
+ Or if there is an attempt to set an inactive control and the driver is
+ not capable of keeping the new value until the control is active again.
+ This is the case for drivers that do not use the standard control
+ framework and rely purely on the hardware to keep the controls' state.
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 b9c62affbb5a..bb7de7a25241 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
@@ -438,3 +438,8 @@ EACCES

Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the
device does not support requests.
+
+ Or if there is an attempt to set an inactive control and the driver is
+ not capable of keeping the new value until the control is active again.
+ This is the case for drivers that do not use the standard control
+ framework and rely purely on the hardware to keep the controls' state.
--
2.31.0.291.g576ba9dcdaf-goog