mirror of https://gitee.com/openkylin/linux.git
30 lines
1.4 KiB
ReStructuredText
30 lines
1.4 KiB
ReStructuredText
|
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.
|