1V4L2 clocks 2----------- 3 4.. attention:: 5 6 This is a temporary API and it shall be replaced by the generic 7 clock API, when the latter becomes widely available. 8 9Many subdevices, like camera sensors, TV decoders and encoders, need a clock 10signal to be supplied by the system. Often this clock is supplied by the 11respective bridge device. The Linux kernel provides a Common Clock Framework for 12this purpose. However, it is not (yet) available on all architectures. Besides, 13the nature of the multi-functional (clock, data + synchronisation, I2C control) 14connection of subdevices to the system might impose special requirements on the 15clock API usage. E.g. V4L2 has to support clock provider driver unregistration 16while a subdevice driver is holding a reference to the clock. For these reasons 17a V4L2 clock helper API has been developed and is provided to bridge and 18subdevice drivers. 19 20The API consists of two parts: two functions to register and unregister a V4L2 21clock source: v4l2_clk_register() and v4l2_clk_unregister() and calls to control 22a clock object, similar to the respective generic clock API calls: 23v4l2_clk_get(), v4l2_clk_put(), v4l2_clk_enable(), v4l2_clk_disable(), 24v4l2_clk_get_rate(), and v4l2_clk_set_rate(). Clock suppliers have to provide 25clock operations that will be called when clock users invoke respective API 26methods. 27 28It is expected that once the CCF becomes available on all relevant 29architectures this API will be removed. 30