linux-kernel - [PATCHv5 2/5] media: v4l UAPI: document ROI selection targets

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Date:   Sat,  1 May 2021 17:19:58 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Ricardo Ribalda <ribalda@...omium.org>
Cc:     Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCHv5 2/5] media: v4l UAPI: document ROI selection targets

Document V4L2 selection targets that will be used to ROI
implementation.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 .../media/v4l/selection-api-configuration.rst | 22 +++++++++++++++
 .../media/v4l/selection-api-examples.rst      | 27 +++++++++++++++++++
 .../media/v4l/v4l2-selection-targets.rst      | 24 +++++++++++++++++
 3 files changed, 73 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/selection-api-configuration.rst b/Documentation/userspace-api/media/v4l/selection-api-configuration.rst
index fee49bf1a1c0..b5fdd765e2db 100644
--- a/Documentation/userspace-api/media/v4l/selection-api-configuration.rst
+++ b/Documentation/userspace-api/media/v4l/selection-api-configuration.rst
@@ -135,3 +135,25 @@ and the height of rectangles obtained using ``V4L2_SEL_TGT_CROP`` and
 ``V4L2_SEL_TGT_COMPOSE`` targets. If these are not equal then the
 scaling is applied. The application can compute the scaling ratios using
 these values.
+
+Configuration of Region of Interest (ROI)
+=========================================
+
+The range of auto-controls values and of coordinates of the top left
+corner, width and height of areas that can be ROI is given by the
+``V4L2_SEL_TGT_ROI_BOUNDS_MIN`` and ``V4L2_SEL_TGT_ROI_BOUNDS_MAX``
+targets. It is recommended for the driver developers to put the top/left
+corner at position ``(0,0)``.
+
+The top left corner, width and height of the Region of Interest area
+and auto-controls currently being employed by the device are given by
+the ``V4L2_SEL_TGT_ROI`` target. It uses the same coordinate system
+as ``V4L2_SEL_TGT_ROI_BOUNDS_MIN`` and ``V4L2_SEL_TGT_ROI_BOUNDS_MAX``.
+
+In order to change active ROI top left, width and height coordinates
+and ROI auto-controls use ``V4L2_SEL_TGT_ROI`` target.
+
+Each capture device has a default ROI rectangle and auto-controls
+value given by the ``V4L2_SEL_TGT_ROI_DEFAULT`` target. Drivers shall
+set the ROI rectangle to the default when the driver is first loaded,
+but not later.
diff --git a/Documentation/userspace-api/media/v4l/selection-api-examples.rst b/Documentation/userspace-api/media/v4l/selection-api-examples.rst
index 5f8e8a1f59d7..39aba98d55f1 100644
--- a/Documentation/userspace-api/media/v4l/selection-api-examples.rst
+++ b/Documentation/userspace-api/media/v4l/selection-api-examples.rst
@@ -82,3 +82,30 @@ Example: Querying for scaling factors
 	/* computing scaling factors */
 	hscale = (double)compose.r.width / crop.r.width;
 	vscale = (double)compose.r.height / crop.r.height;
+
+Setting Region Of Interest area to half of the default value
+
+Example: Simple ROI
+===========================
+
+.. code-block:: c
+
+	struct v4l2_selection roi = {
+	    .type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
+	    .target = V4L2_SEL_TGT_ROI_DEFAULT,
+	};
+	struct v4l2_rect r;
+
+	ret = ioctl(fd, VIDIOC_G_SELECTION, &roi);
+	if (ret)
+	    exit(-1);
+	/* setting smaller ROI rectangle */
+	r.width = roi.r.width / 2;
+	r.height = roi.r.height / 2;
+	r.left = roi.r.width / 4;
+	r.top = roi.r.height / 4;
+	roi.r = r;
+	roi.target = V4L2_SEL_TGT_ROI;
+	ret = ioctl(fd, VIDIOC_S_SELECTION, &roi);
+	if (ret)
+	    exit(-1);
diff --git a/Documentation/userspace-api/media/v4l/v4l2-selection-targets.rst b/Documentation/userspace-api/media/v4l/v4l2-selection-targets.rst
index b46bae984f35..d1dc9c50eb05 100644
--- a/Documentation/userspace-api/media/v4l/v4l2-selection-targets.rst
+++ b/Documentation/userspace-api/media/v4l/v4l2-selection-targets.rst
@@ -75,6 +75,30 @@ of the two interfaces they are used.
 	modified by hardware.
       - Yes
       - No
+    * - ``V4L2_SEL_TGT_ROI``
+      - 0x0200
+      - Current Region of Interest rectangle and auto-controls value.
+      - Yes
+      - No
+    * - ``V4L2_SEL_TGT_ROI_DEFAULT``
+      - 0x0201
+      - Suggested Region of Interest rectangle and auto-controls value.
+      - Yes
+      - No
+    * - ``V4L2_SEL_TGT_ROI_BOUNDS_MIN``
+      - 0x0202
+      - Minimum bounds of the Region of Interest rectangle and minimum
+	auto-controls value. All valid ROI rectangles and auto-controls
+	should be within minimum-maximum range.
+      - Yes
+      - No
+    * - ``V4L2_SEL_TGT_ROI_BOUNDS_MAX``
+      - 0x0203
+      - Maximum bounds of the Region of Interest rectangle and maximum
+	auto-controls value. All valid ROI rectangles and auto-controls
+	should be within minimum-maximum range.
+      - Yes
+      - No
 
 .. raw:: latex
 
-- 
2.31.1.527.g47e6f16901-goog