30 lines
1.4 KiB
ReStructuredText
30 lines
1.4 KiB
ReStructuredText
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V4L2 clocks
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-----------
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.. attention::
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This is a temporary API and it shall be replaced by the generic
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clock API, when the latter becomes widely available.
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Many subdevices, like camera sensors, TV decoders and encoders, need a clock
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signal to be supplied by the system. Often this clock is supplied by the
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respective bridge device. The Linux kernel provides a Common Clock Framework for
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this purpose. However, it is not (yet) available on all architectures. Besides,
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the nature of the multi-functional (clock, data + synchronisation, I2C control)
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connection of subdevices to the system might impose special requirements on the
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clock API usage. E.g. V4L2 has to support clock provider driver unregistration
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while a subdevice driver is holding a reference to the clock. For these reasons
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a V4L2 clock helper API has been developed and is provided to bridge and
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subdevice drivers.
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The API consists of two parts: two functions to register and unregister a V4L2
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clock source: v4l2_clk_register() and v4l2_clk_unregister() and calls to control
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a clock object, similar to the respective generic clock API calls:
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v4l2_clk_get(), v4l2_clk_put(), v4l2_clk_enable(), v4l2_clk_disable(),
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v4l2_clk_get_rate(), and v4l2_clk_set_rate(). Clock suppliers have to provide
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clock operations that will be called when clock users invoke respective API
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methods.
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It is expected that once the CCF becomes available on all relevant
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architectures this API will be removed.
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