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media: Documentation: v4l: Improve frame rate configuration documentation 

Improve the documentation of the frame rate configuration so that it can
be understood by a regular human being.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Sakari Ailus 2021-06-22 13:17:20 +02:00 committed by Mauro Carvalho Chehab
parent 8925b53083
commit e5a466d4bc
1 changed files with 10 additions and 13 deletions
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23
Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst
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@ -23,19 +23,7 @@ Image Process Control IDs
.. _v4l2-cid-link-freq:
``V4L2_CID_LINK_FREQ (integer menu)``
Data bus frequency. Together with the media bus pixel code, bus type
(clock cycles per sample), the data bus frequency defines the pixel
rate (``V4L2_CID_PIXEL_RATE``) in the pixel array (or possibly
elsewhere, if the device is not an image sensor). The frame rate can
be calculated from the pixel clock, image width and height and
horizontal and vertical blanking. While the pixel rate control may
be defined elsewhere than in the subdev containing the pixel array,
the frame rate cannot be obtained from that information. This is
because only on the pixel array it can be assumed that the vertical
and horizontal blanking information is exact: no other blanking is
allowed in the pixel array. The selection of frame rate is performed
by selecting the desired horizontal and vertical blanking. The unit
of this control is Hz.
The frequency of the data bus (e.g. parallel or CSI-2).
.. _v4l2-cid-pixel-rate:
@ -43,6 +31,15 @@ Image Process Control IDs
Pixel sampling rate in the device's pixel array. This control is
read-only and its unit is pixels / second.
Some devices use horizontal and vertical balanking to configure the frame
rate. The frame rate can be calculated from the pixel rate, analogue crop
rectangle as well as horizontal and vertical blanking. The pixel rate
control may be present in a different sub-device than the blanking controls
and the analogue crop rectangle configuration.
The configuration of the frame rate is performed by selecting the desired
horizontal and vertical blanking. The unit of this control is Hz.
``V4L2_CID_TEST_PATTERN (menu)``
Some capture/display/sensor devices have the capability to generate
test pattern images. These hardware specific test patterns can be