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b67b81d750
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: Mauro Carvalho Chehab <mchehab@s-opensource.com>
30 lines
1.4 KiB
ReStructuredText
30 lines
1.4 KiB
ReStructuredText
V4L2 clocks
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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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