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media: Documentation: v4l: Document required controls on camera sensors

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Raw camera sensors connected to parallel or CSI-2 busses need to implement
V4L2_CID_LINK_FREQ control so receiver drivers can configure the hardware
accordingly.

Document this. Also say V4L2_CID_PIXEL_RATE is recommended for such
hardware.

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 2020-10-13 16:02:27 +02:00 committed by Mauro Carvalho Chehab
parent d3ed195bc7
commit 9d0a79e55a
1 changed files with 13 additions and 0 deletions
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13
Documentation/driver-api/media/camera-sensor.rst
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@ -132,3 +132,16 @@ used to obtain device's power state after the power state transition:
The function returns a non-zero value if it succeeded getting the power count or
runtime PM was disabled, in either of which cases the driver may proceed to
access the device.
Controls
--------
For camera sensors that are connected to a bus where transmitter and receiver
require common configuration set by drivers, such as CSI-2 or parallel (BT.601
or BT.656) bus, the ``V4L2_CID_LINK_FREQ`` control is mandatory on transmitter
drivers. Receiver drivers can use the ``V4L2_CID_LINK_FREQ`` to query the
frequency used on the bus.
The transmitter drivers should also implement ``V4L2_CID_PIXEL_RATE`` control in
order to tell the maximum pixel rate to the receiver. This is required on raw
camera sensors.