[U-Boot] [PATCH v7 5/9] arm: serial: Add ability to use pre-initialized UARTs

[Rob Herring]

On Wed, Oct 14, 2015 at 11:55 AM, Sergey Temerkhanov
<s.temerkhanov at gmail.com> wrote:
> On some systems, UART initialization is performed before running U-Boot.
> This commit allows to skip UART re-initializaion on those systems
>
> Signed-off-by: Sergey Temerkhanov <s.temerkhanov at gmail.com>
> Signed-off-by: Radha Mohan Chintakuntla <rchintakuntla at cavium.com>
>
> Reviewed-by: Simon Glass <sjg at chromium.org>

I'll comment on this now that I'm here, but as the rest of the thread
said, please send to DT list.

> diff --git a/doc/device-tree-bindings/serial/pl01x.txt b/doc/device-tree-bindings/serial/pl01x.txt
> index 61c27d1..0591497 100644
> --- a/doc/device-tree-bindings/serial/pl01x.txt
> +++ b/doc/device-tree-bindings/serial/pl01x.txt
> @@ -5,3 +5,6 @@ Required properties:
>  - reg: exactly one register range with length 0x1000
>  - clock: input clock frequency for the UART (used to calculate the baud
>    rate divisor)
> +
> +Optional properties:
> +- u-boot,skip-init: skip UART initialization at start.

What are you trying to accomplish by skipping?

stdout-path can take options now, so what about making it an option there:

stdout-path = &serial0:no-init

I have similar concerns with this as I did with the early init flag.
This requires the dtb and u-boot to be in sync. For example, you have
this option in the dtb, but then you add clock initialization to your
platform which changes the default clock frequency of the UART. Now if
you boot with an older dtb and new u-boot, then it will break because
the UART is at the wrong baudrate.

Rob