![Mauro Carvalho Chehab](/assets/img/avatar_default.png)
All Documentation files outside the uAPI are all licensed with, at least, GPL 2.0. So, mark them as such. The ondes at media/uapi are at least GFDL 1.1+. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
32 lines
1.5 KiB
ReStructuredText
32 lines
1.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
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.
|