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

[Graeme Russ]

Hi Simon,

On Tue, Mar 20, 2012 at 7:27 AM, Simon Glass <sjg at chromium.org> wrote:
> This patch adds support for console output in the event of a panic() before
> the console is inited. The main purpose of this is to deal with a very early
> panic() which would otherwise cause a silent hang.
>
> A new board_pre_console_panic() function is added to the board API. If
> provided by the board it will be called in the event of a panic before the
> console is ready. This function should turn on all available UARTs and
> output the string (plus a newline) if it possibly can.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---

>  void panic(const char *fmt, ...)
>  {
> +       char str[CONFIG_SYS_PBSIZE];
>        va_list args;
> +
>        va_start(args, fmt);
> -       vprintf(fmt, args);
> -       putc('\n');
> +       vsnprintf(str, sizeof(str), fmt, args);
>        va_end(args);
> +
> +       if (gd->have_console) {
> +               puts(str);
> +               putc('\n');
> +       } else {
> +               board_pre_console_panic(str);
> +       }
> +

Would there be benefit in including an option to dump the pre-console
buffer (if one is enabled) - I think it's contents could be rather useful
in debugging what went wrong...

And something is nagging at me that the API is just 'not right'. I don't
know exactly why, but I really don't like how this is plumbed

panic() calls putc() which, if we do not have a console (and we won't in
the case of the early panic case we are dealing with), will be put into
the pre console buffer (if enabled)

So having panic() call a board specific function to dump the pre console
buffer after the  vprintf() / putc() would achieve the same result (but
you need pre console buffer enabled)

So, if CONFIG_PRE_CONSOLE_BUFFER is defined, we could simply add a call to
dump_pre_console_buffer() at the end of panic(). But we already have a
function to do that - print_pre_console_buffer(). If we added an argument
to print_pre_console_buffer() which is a pointer to a 'putc()' type
function (NULL meaning the standard putc()) and that function lived in the
board files then life would be good. We could also add a call to a setup
function so we are not setting up the UARTS every putc (not that
performance is a priority at this stage, but some boards might quibble
about hitting certain registers continuously)

But what to do if pre console buffer is not defined? The panic message
needs to be sent directly to the 'panic UARTS'...

OK, so what about in panic():
 - If gd->have_console is not set:
    o call the board specific setup_panic_uarts()
    o call print_pre_console_buffer() passing panic_putc()
    o call panic_putc() for all characters in str[]
 - If gd->have_console is set:
    o call putc() for all characters in str[]

setup_panic_uarts() and panic_putc() are overriden in the board files

Regards,

Graeme