[U-Boot] [PATCH v4] Add board_pre_console_putc to deal with early console output

[Simon Glass]

Hi Stefan,

On Sun, Dec 4, 2011 at 10:56 AM, Stefano Babic <sbabic at denx.de> wrote:
> On 02/12/2011 19:16, Simon Glass wrote:
>
>> It actually started as a last-ditch panic message printer. It morphed
>> into the general pre-console putc after discussions on the list (with
>> Graeme).
>>
>> It can happen that your early board code does not know what clocks to
>> use, or can't find a console, or some other critical error. It then
>> calls panic() which silently dies or maybe reboots if you are lucky.
>> This problem mostly comes about with device trees, where we must have
>> certain info in the device tree before we can even get to relocation.
>>
>> The idea is that boards provide a way of outputting characters which
>> tries to work on all types of boards with that SOC. For example, they
>> output the characters on all UARTs with various clock options, etc.
>>
>> We use it on Tegra to print a friendly panic message when something is
>> horribly wrong. In this case we will never make it to relocation so
>> the pre-console buffer will not be displayed. So we can't rely on
>> that.
>
> I do not know if this mechanism can be used on other SOCs, but IMHO it
> does not hurt and it helps at least on Tegra, as you explained me.
>
> Applied to u-boot-staging, sbabic at denx.de branch

Thanks. I think it can be used on any SOC with internal UARTs and a
reasonably small list of permitted clock speeds. I suspect I will be
trying it out on a few before long.

Regards,
Simon

>
> Best regards,
> Stefano Babic
>
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