Previously ns16550 compatible UARTs probed via device tree have needed
their device tree nodes to contain a clock-frequency property. An
alternative to this commonly used with Linux is to reference a clock via
a phandle. This patch allows U-Boot to support that, retrieving the
clock frequency by probing the appropriate clock device.
For example, a system might choose to provide the UART base clock as a
reference to a clock common to multiple devices:
sys_clk: clock {
compatible = "fixed-clock";
#clock-cells = <0>;
clock-frequency = <10000000>;
};
uart0: uart@10000000 {
compatible = "ns16550a";
reg = <0x10000000 0x1000>;
clocks = <&sys_clk>;
};
uart1: uart@10000000 {
compatible = "ns16550a";
reg = <0x10001000 0x1000>;
clocks = <&sys_clk>;
};
This removes the need for the frequency information to be duplicated in
multiple nodes and allows the device tree to be more descriptive of the
system.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
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