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

[Simon Glass]

Hi Graeme,

On Sun, Dec 4, 2011 at 7:40 PM, Graeme Russ <graeme.russ at gmail.com> wrote:
> 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

It could have been when it was still a pre-console panic. But now that
it has morphed into a general putc(), I suppose the only option is to
somehow detect the first call and send the pre-console text first?

Regards,
Simon

>
> Regards,
>
> Graeme
>