u-boot/drivers/clk/Kconfig
Simon Glass f26c8a8e77 dm: Add a clock uclass
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>
2015-07-21 17:39:29 -06:00

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config CLK
bool "Enable clock driver support"
depends on DM
help
This allows drivers to be provided for clock generators, including
oscillators and PLLs. Devices can use a common clock API to request
a particular clock rate and check on available clocks. Clocks can
feed into other clocks in a tree structure, with multiplexers to
choose the source for each clock.
config SPL_CLK_SUPPORT
bool "Enable clock support in SPL"
depends on CLK
help
The clock subsystem adds a small amount of overhead to the image.
If this is acceptable and you have a need to use clock drivers in
SPL, enable this option. It might provide a cleaner interface to
setting up clocks within SPL, and allows the same drivers to be
used as U-Boot proper.