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

[Simon Glass]

Hi Rob,

On 19 October 2015 at 14:14, Rob Herring <robherring2 at gmail.com> wrote:
> 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.

If you are saying what I think you are saying, U-Boot expects the
device tree that IT uses for configuration to come from the same
commit as the source code. It doesn't support anything else as the DTB
is bundled with (and replaced at the same time as) U-Boot.. You would
be on your own in that case.

Regards,
Simon