[U-Boot] AM335x configurations - console output at early stages lost

[Simon Glass]

Hi Vasili,

On 29 April 2015 at 10:57, Vasili Galka <vvv444 at gmail.com> wrote:
> Hi Tom,
>
> I’m working on rebasing an old U-Boot branch for our company’s AM335x
> based board upon the current U-Boot release (v2015.04). Our branch was
> initially based on the v2013.10 release (the ti/am335x/ board was
> taken as reference).
>
> After making all the code compile, I discovered there was a change in
> the U-Boot initialization sequence, introduced by commit
> a6b541b09022acb6f7c2754100ae26bd44eed1d9, that prevents our code from
> working:
>
> Prior to the above mentioned commit, the console serial port was
> initialized at a very early stage in the armv7/am335x/board.c:s_init()
> function (calling preloader_console_init()). Roughly saying, it was
> the first thing done by the SPL code. This made quite much sense, as
> it enabled all the code afterwards to output status/debugging info to
> the console.
> Moving the preloader_console_init() call to spl_board_init() caused it
> to be run at a very "late" stage (as part of the board_init_r()
> function). AFAIU, now all the code that runs till then has no ability
> for any console output.
> For example, in our particular case, the DDR configuration code (in
> sdram_init()) reads the DDR type from an I2C EEPROM. Obviously, if
> something goes wrong in this process, we would like to report it to
> the console.
>
> I understand there was a good reason for the mentioned commit (the
> GD), however, as you see, we have also lost some important
> functionality with it. I would appreciate your advice on how to solve
> it.

It would certainly be very useful and it would be great if we could
printf() from as soon as we have a stack (and perhaps printch() even
earlier). I think it can be done, but I have not put in the time to
figure it out.

You could take a look at CONFIG_DEBUG_UART which at least allows
primitive UART access before gd is set up. I wonder if we could do
something like change printf() /purchatr() to use this when gd is
NULL?

Regards,
Simon