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Commit b67b81d7 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
Browse files

[media] move V4L2 clocks to a separate .rst file 



Move the v4l2 clocks stuff from v4l2-framework to a separate
file and adds an attention that came from the v4l2-clk.h.

Note: as this is meant to be a temporary kAPI, and it is
used only by two drivers (soc_camera and em28xx), where
the first one is in deprecation process, it probably not
a worth effort to document its header.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent 46f74f1d

Documentation/media/kapi/v4l2-clocks.rst

0 → 100644
+29 −0
Original line number Diff line number Diff line 
V4L2 clocks

-----------



.. attention::



	This is a temporary API and it shall be replaced by the generic

	clock API, when the latter becomes widely available.



Many subdevices, like camera sensors, TV decoders and encoders, need a clock

signal to be supplied by the system. Often this clock is supplied by the

respective bridge device. The Linux kernel provides a Common Clock Framework for

this purpose. However, it is not (yet) available on all architectures. Besides,

the nature of the multi-functional (clock, data + synchronisation, I2C control)

connection of subdevices to the system might impose special requirements on the

clock API usage. E.g. V4L2 has to support clock provider driver unregistration

while a subdevice driver is holding a reference to the clock. For these reasons

a V4L2 clock helper API has been developed and is provided to bridge and

subdevice drivers.



The API consists of two parts: two functions to register and unregister a V4L2

clock source: v4l2_clk_register() and v4l2_clk_unregister() and calls to control

a clock object, similar to the respective generic clock API calls:

v4l2_clk_get(), v4l2_clk_put(), v4l2_clk_enable(), v4l2_clk_disable(),

v4l2_clk_get_rate(), and v4l2_clk_set_rate(). Clock suppliers have to provide

clock operations that will be called when clock users invoke respective API

methods.



It is expected that once the CCF becomes available on all relevant

architectures this API will be removed.

Documentation/media/kapi/v4l2-core.rst

+1 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ Video2Linux devices 
    v4l2-controls

    v4l2-device

    v4l2-fh

    v4l2-clocks

    v4l2-dv-timings

    v4l2-event

    v4l2-flash-led-class

Documentation/media/kapi/v4l2-framework.rst

+0 −25
Original line number Diff line number Diff line
@@ -79,28 +79,3 @@ and the v4l2_fh struct keeps track of filehandle instances. 
The V4L2 framework also optionally integrates with the media framework. If a

driver sets the struct v4l2_device mdev field, sub-devices and video nodes

will automatically appear in the media framework as entities.
 


V4L2 clocks

-----------



Many subdevices, like camera sensors, TV decoders and encoders, need a clock

signal to be supplied by the system. Often this clock is supplied by the

respective bridge device. The Linux kernel provides a Common Clock Framework for

this purpose. However, it is not (yet) available on all architectures. Besides,

the nature of the multi-functional (clock, data + synchronisation, I2C control)

connection of subdevices to the system might impose special requirements on the

clock API usage. E.g. V4L2 has to support clock provider driver unregistration

while a subdevice driver is holding a reference to the clock. For these reasons

a V4L2 clock helper API has been developed and is provided to bridge and

subdevice drivers.



The API consists of two parts: two functions to register and unregister a V4L2

clock source: v4l2_clk_register() and v4l2_clk_unregister() and calls to control

a clock object, similar to the respective generic clock API calls:

v4l2_clk_get(), v4l2_clk_put(), v4l2_clk_enable(), v4l2_clk_disable(),

v4l2_clk_get_rate(), and v4l2_clk_set_rate(). Clock suppliers have to provide

clock operations that will be called when clock users invoke respective API

methods.



It is expected that once the CCF becomes available on all relevant

architectures this API will be removed.