linux-kernel - [PATCH v8 17/19] media: docs: Document the behaviour of uvcdriver

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Date:   Fri, 19 Mar 2021 18:09:04 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        tfiga@...omium.org
Cc:     Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH v8 17/19] media: docs: Document the behaviour of uvcdriver

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@...omium.org>
---
 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.rc2.261.g7f71774620-goog