Early debug UART not working on AM33XX SoC

[Felix Brack]

Hello Simon

On 27.01.22 18:33, Simon Glass wrote:
> 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.
>
I will check that. Maybe the board_debug_uart_init() is not the right
place then as it is board specific. Probably better to have a AM33XX
platform specific function.

Having said that there is still something I don't understand: commit
0dba4586 has added a call to debug_uart_init() in crt0.S but not removed
any existing call to debug_uart_init(). Hence this function is called twice.
Is this intentional (and if so, why ?) or are the remaining calls some
sort of leftovers?

>> 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

-- 
Regards, Felix