[PATCH 0/3] ARM: dts: stm32: lxa: change stdout-path baud rate from 9600 to 115200

[Ahmad Fatoum]

Hello David,

On 6/12/26 8:53 AM, David Laight wrote:
> On Thu, 11 Jun 2026 22:33:18 +0200
> Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
> 
>> Hi David,
>>
>> On 6/11/26 21:43, David Laight wrote:
>>> On Thu, 11 Jun 2026 20:12:32 +0200
>>> Ahmad Fatoum <a.fatoum at pengutronix.de> wrote:
>>>   
>>>> The LXA boards are the only STM32 boards that set stdout-path = &uart*
>>>> instead of explicitly specifying a baud rate.
>>>>
>>>> This would mean the default of 9600 is used, but it goes unnoticed when
>>>> booting normally as barebox fixes up a console= line that includes a
>>>> baud rate.
>>>>
>>>> When EFI booting GRUB however, GRUB will not pass along the console=
>>>> line and thus the board ends up with a 9600 baud Linux console,
>>>> confusing users.  
>>>
>>> Is it possible to determine the current baud rate (by reading the hardware
>>> register) and default to that value.
>>> Then if grub has initialised the uart the kernel will use the same
>>> baud rate.  
>>
>> I think so, yes. In addition to the register divider configuration, one
>> would need the input clock rate as well, but that's not a problem.
>>
>> Do you know if any drivers already do this?
> 
> I've seen it done somewhere, certainly x86, but possibly NetBSD.
> That would have been preserving the baud rate set by the bios.
> You don't want the baud rate changing half way through the boot sequence.

I agree in general, but in this case here, the BIOS defaults to 115200:

https://github.com/linux-automation/meta-lxatac/blob/wrynose/meta-lxatac-bsp/recipes-bsp/barebox/files/lxatac/defconfig#L171
https://elixir.bootlin.com/barebox/v2026.06.0/source/common/console.c#L349

Cheers,
Ahmad

> 
> 	David
> 
>>
>> Nevertheless, I would like the LXA device trees changed, even if only
>> to align them with all other existing STM32 device trees.
>>
>> Cheers,
>> Ahmad
>>
>>
>>>
>>> 	David
>>>   
>>>>
>>>> This series fixes this. As the device trees were added at different
>>>> times, they are fixed each in a separate commit with its own Fixes: tag.
>>>>
>>>> ---
>>>> Ahmad Fatoum (3):
>>>>       ARM: dts: stm32: lxa-mc1: change stdout-path baud rate from 9600 to 115200
>>>>       ARM: dts: stm32: lxa-tac: change stdout-path baud rate from 9600 to 115200
>>>>       ARM: dts: stm32: fairytux2: change stdout-path baud rate from 9600 to 115200
>>>>
>>>>  arch/arm/boot/dts/st/stm32mp153c-lxa-fairytux2.dtsi | 2 +-
>>>>  arch/arm/boot/dts/st/stm32mp157c-lxa-mc1.dts        | 2 +-
>>>>  arch/arm/boot/dts/st/stm32mp15xc-lxa-tac.dtsi       | 2 +-
>>>>  3 files changed, 3 insertions(+), 3 deletions(-)
>>>> ---
>>>> base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48
>>>> change-id: 20260611-lxa-stdout-path-baudrate-7cf454cdae07
>>>>
>>>> Best regards,
>>>> --  
>>>> Ahmad Fatoum <a.fatoum at pengutronix.de>
>>>>
>>>>  
>>>
>>>   
>>
>>
> 
> 

-- 
Pengutronix e.K.                  |                             |
Steuerwalder Str. 21              | http://www.pengutronix.de/  |
31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |