Fix compile warning for non OF_CONTROL builds:

---8<---
In file included from /Volumes/devel/u-boot/drivers/gpio/atmel_pio4.c:10:0:
/Volumes/devel/u-boot/include/clk.h:107:12: warning: 'clk_get_by_name' defined but not used [-Wunused-function]
--->8---

Signed-off-by: Andreas Bießmann <andreas@biessmann.org>
Acked-by: Stephen Warren <swarren@nvidia.com>

Add support for this feature in the core clock code.

Signed-off-by: Simon Glass <sjg@chromium.org>

The following changes are made to the clock API:
* The concept of "clocks" and "peripheral clocks" are unified; each clock
  provider now implements a single set of clocks. This provides a simpler
  conceptual interface to clients, and better aligns with device tree
  clock bindings.
* Clocks are now identified with a single "struct clk", rather than
  requiring clients to store the clock provider device and clock identity
  values separately. For simple clock consumers, this isolates clients
  from internal details of the clock API.
* clk.h is split so it only contains the client/consumer API, whereas
  clk-uclass.h contains the provider API. This aligns with the recently
  added reset and mailbox APIs.
* clk_ops .of_xlate(), .request(), and .free() are added so providers
  can customize these operations if needed. This also aligns with the
  recently added reset and mailbox APIs.
* clk_disable() is added.
* All users of the current clock APIs are updated.
* Sandbox clock tests are updated to exercise clock lookup via DT, and
  clock enable/disable.
* rkclk_get_clk() is removed and replaced with standard APIs.

Buildman shows no clock-related errors for any board for which buildman
can download a toolchain.

test/py passes for sandbox (which invokes the dm clk test amongst
others).

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

Add a method which can locate a clock for a device, given its index. This
uses the normal device tree bindings to return the clock device and the
first argument which is normally used as a peripheral ID in U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>

The most basic thing for clock is to enable it, but it is missing
in this uclass.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>

This header uses ulong, so it needs to include <linux/types.h>.
Likewise, "struct udevice" must be declared before it is used.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>

The comment about get_periph_rate() is the same as that of
set_periph_rate().

I am fixing typos here and there while I am in this file.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>

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>

Command provides just dump subcommand for showing clock
frequencies in a soc.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Stefano Babic <sbabic@denx.de>