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

[David Laight <david.laight.linux@gmail.com>]

On Thu, 11 Jun 2026 22:33:18 +0200
Ahmad Fatoum <a.fatoum@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@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.

	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@pengutronix.de>
> >>
> >>  
> > 
> >   
> 
>