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Clocks are an important feature of platforms and have become increasing complex with time. Most modern SoCs have multiple PLLs and dozens of clock dividers which distribute clocks to on-chip peripherals. Some SoC implementations have a clock API which is private to that SoC family, e.g. Tegra and Exynos. This is useful but it would be better to have a common API that can be understood and used throughout U-Boot. Add a simple clock API as a starting point. It supports querying and setting the rate of a clock. Each clock is a device. To reduce memory and processing overhead the concept of peripheral clocks is provided. These do not need to be explicit devices - it is possible to write a driver that can adjust the I2C clock (for example) without an explicit I2C clock device. This can dramatically reduce the number of devices (and associated overhead) in a complex SoC. Clocks are referenced by a number, and it is expected that SoCs will define that numbering themselves via an enum. Signed-off-by: Simon Glass <sjg@chromium.org>
19 lines
764 B
Text
19 lines
764 B
Text
config CLK
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bool "Enable clock driver support"
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depends on DM
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help
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This allows drivers to be provided for clock generators, including
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oscillators and PLLs. Devices can use a common clock API to request
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a particular clock rate and check on available clocks. Clocks can
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feed into other clocks in a tree structure, with multiplexers to
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choose the source for each clock.
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config SPL_CLK_SUPPORT
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bool "Enable clock support in SPL"
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depends on CLK
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help
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The clock subsystem adds a small amount of overhead to the image.
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If this is acceptable and you have a need to use clock drivers in
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SPL, enable this option. It might provide a cleaner interface to
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setting up clocks within SPL, and allows the same drivers to be
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used as U-Boot proper.
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