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

[Graeme Russ]

Hi Simon,

On Mon, Dec 5, 2011 at 2:34 PM, Simon Glass <sjg at chromium.org> wrote:
> 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.

Can it be used in conjuction with PRE_CONSOLE_BUFFER? i.e. panic()
prints the contents of the PRE_CONSOLE_BUFFER before the panic
message? I think that would be invaluable in determining what was
happening leading up to the panic

Regards,

Graeme