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Documentation: media: camera-sensor: Move power management section

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Move the power management section up, just after clocks, as it relates
to internal system resources and not features exposed to applications.
The text itself is otherwise unchanged.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
This commit is contained in:
Laurent Pinchart 2023-09-14 21:16:40 +03:00 committed by Hans Verkuil
parent 6d032832b1
commit f13734b507
1 changed files with 35 additions and 35 deletions
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70
Documentation/driver-api/media/camera-sensor.rst
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@ -43,6 +43,41 @@ hasn't been modified directly or indirectly by another driver, or supported by
the board's clock tree to begin with. Changes to the Common Clock Framework API
are required to ensure reliability.
Power management
----------------
Always use runtime PM to manage the power states of your device. Camera sensor
drivers are in no way special in this respect: they are responsible for
controlling the power state of the device they otherwise control as well. In
general, the device shall be powered on at least when its registers are being
accessed and when it is streaming.
Existing camera sensor drivers may rely on the old
struct v4l2_subdev_core_ops->s_power() callback for bridge or ISP drivers to
manage their power state. This is however **deprecated**. If you feel you need
to begin calling an s_power from an ISP or a bridge driver, instead please add
runtime PM support to the sensor driver you are using. Likewise, new drivers
should not use s_power.
Please see examples in e.g. ``drivers/media/i2c/ov8856.c`` and
``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI
and DT based systems.
Control framework
~~~~~~~~~~~~~~~~~
``v4l2_ctrl_handler_setup()`` function may not be used in the device's runtime
PM ``runtime_resume`` callback, as it has no way to figure out the power state
of the device. This is because the power state of the device is only changed
after the power state transition has taken place. The ``s_ctrl`` callback can be
used to obtain device's power state after the power state transition:
.. c:function:: int pm_runtime_get_if_in_use(struct device *dev);
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.
Frame size
----------
@ -118,41 +153,6 @@ rate) on device level in firmware or hardware. This means lower level controls
implemented by raw cameras may not be used on uAPI (or even kAPI) to control the
frame interval on these devices.
Power management
----------------
Always use runtime PM to manage the power states of your device. Camera sensor
drivers are in no way special in this respect: they are responsible for
controlling the power state of the device they otherwise control as well. In
general, the device shall be powered on at least when its registers are being
accessed and when it is streaming.
Existing camera sensor drivers may rely on the old
struct v4l2_subdev_core_ops->s_power() callback for bridge or ISP drivers to
manage their power state. This is however **deprecated**. If you feel you need
to begin calling an s_power from an ISP or a bridge driver, instead please add
runtime PM support to the sensor driver you are using. Likewise, new drivers
should not use s_power.
Please see examples in e.g. ``drivers/media/i2c/ov8856.c`` and
``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI
and DT based systems.
Control framework
~~~~~~~~~~~~~~~~~
``v4l2_ctrl_handler_setup()`` function may not be used in the device's runtime
PM ``runtime_resume`` callback, as it has no way to figure out the power state
of the device. This is because the power state of the device is only changed
after the power state transition has taken place. The ``s_ctrl`` callback can be
used to obtain device's power state after the power state transition:
.. c:function:: int pm_runtime_get_if_in_use(struct device *dev);
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.
Rotation, orientation and flipping
----------------------------------