Early debug UART not working on AM33XX SoC

[Simon Glass]

Hi Felix,

On Thu, 27 Jan 2022 at 09:27, Felix Brack <fb at ltec.ch> wrote:
>
> Hello Simon,
>
> On 27.01.22 16:05, Simon Glass wrote:
> > Hi Felix,
> >
> > On Wed, 26 Jan 2022 at 07:02, Felix Brack <fb at ltec.ch> wrote:
> >>
> >> Hello Simon,
> >>
> >> I am trying to get the current U-Boot master working on the PDU001
> >> board. This involves the use of an early debug UART.
> >>
> >> With commit 0dba4586 (arm: Init the debug UART) the early debug UART on
> >> the AM33XX SoC doesn't work anymore.
> >>
> >> By looking at the code involved I believe a call to
> >> setup_clocks_for_console() implemented in clock_am33xx.c before the call
> >> to debug_uart_init() is missing. This is also what happens prior to
> >> commit 0dba4586 by a call to early_system_init() which in turn calls
> >> setup_early_clocks() which then calls setup_clocks_for_console().
> >>
> >> My quick and dirty fix consist of inserting a call in crt0.S to
> >> setup_clocks_for_console() just before the call to debug_uart_init()
> >> which was added in commit 0dba4586. I have guarded this call with
> >> #if/#endif testing for CONFIG_AM33XX. The code sequence in crt0.S now
> >> looks like this:
> >>
> >> #if defined(CONFIG_DEBUG_UART) && CONFIG_IS_ENABLED(SERIAL)
> >>   #if defined(CONFIG_AM33XX)
> >>     bl setup_clocks_for_console
> >>   #endif
> >>     bl debug_uart_init
> >> #endif
> >>
> >> However, from what I understand the crt0.S is for _all_ ARM boards hence
> >> it's probably a bad idea polluting it with such #if/#endif tests for
> >> different SoCs. What do you think?
> >>
> >> If my quick and dirty fix is not that dirty I would be happy to send a
> >> patch which would also include the removal of the currently remaining
> >> call to debug_uart_init() in am33xx/board.c
> >>
> >> Please apologize my narrow view of the matter dealing only with AM33XX SoCs.
> >
> > Are you able to put that call into board_debug_uart_init() and enable
> > CONFIG_DEBUG_UART_BOARD_INIT ?
> >
> Sure I can but there two drawbacks:
> 1. this fixes the problem only for my board, others might remain broken

I suggest you make the function common to all boards that need it.

> 2. the now redundant call to setup_early_clocks() in am33xx/board.c
>    remains (at least it does not seem to hurt ;-))

Yes, it is possible to use flags to avoid that, but might not be worth it.

>
> I will prepare a patch with a modified board_debug_uart_init() for the
> PDU001 board then.
>
> --
> Many thanks for your help and kind regards, Felix
>

Regards,
Simon