[U-Boot] [PATCH 2/5] Add board_panic_no_console() to deal with early critical errors

[Wolfgang Denk]

Dear Simon,

In message <CAPnjgZ1TBN+Ro8f0nDubAYRi54UAV0LxjrdFz-AW5qBgue1+Fw at mail.gmail.com> you wrote:
> 
> > Please make up your mind:  either you CAN initialize the console, then
> > you can use it to output messages in a regular way, or you CANNOT
> > initialize it, in which case you cannot print anything.  There is no
> > third option.
>
> Well that is very clear - we cannot. We hit panic() before
> console_ready() is called.

OK - but this means that no output to a serial console port can be
done, no matter what you try.

> > If you have "available UARTs", you could use this as console, right?
>
> Yes, if we knew which it was.

This is a design issue.  If there are several similar boards that
shall be handled with the same binary, then you must agree on some
common sub-set of features, like on UART port that is available on all
of these, and use this as (early) console port.

> We know we won't get to console init in this case - there is a panic()
> that happens first. So the existing pre-console putc() becomes our
> route to displaying a message. The problem with that is only that the

No.  When you cannot initialize the console, you cannot output
anything to the console. Period.

If there is a way to do some initialization and output charatcers,
than make this your regular console init code, and use it always,
without any special warts.

> board init hasn't happened yet, so either the pre-console putc() must
> init the UARTs or we need a separate init function.

This makes no sense to me.

> So the existing pre-console putc() can be used, if we can sort out how
> to make UART init work. Graeme suggested an approach here - I will see
> if I can make that work.

I don't think I will accept any "pre-console putc()".  This is such a
dirty hack.  Either you can initialize and use putc, then use the
normal console mechanism for it, or you cannot. And "cannot" means
"cannot" here.

Best regards,

Wolfgang Denk

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