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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f2ce361sm31634760f8f.31.2026.06.15.02.00.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jun 2026 02:00:38 -0700 (PDT) Date: Mon, 15 Jun 2026 10:00:36 +0100 From: David Laight To: Ahmad Fatoum Cc: Alexandre Torgue , Maxime Coquelin , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Leonard =?UTF-8?B?R8O2aHJz?= , Marc Kleine-Budde , Alexandre Torgue , devicetree@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel@pengutronix.de Subject: Re: [PATCH 0/3] ARM: dts: stm32: lxa: change stdout-path baud rate from 9600 to 115200 Message-ID: <20260615100036.1e09c22d@pumpkin> In-Reply-To: References: <20260611-lxa-stdout-path-baudrate-v1-0-59b60a5069ff@pengutronix.de> <20260611204341.147f1afb@pumpkin> <20260612075342.6615d66c@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 15 Jun 2026 09:53:49 +0200 Ahmad Fatoum wrote: > Hello David, > > On 6/12/26 8:53 AM, David Laight wrote: > > On Thu, 11 Jun 2026 22:33:18 +0200 > > Ahmad Fatoum wrote: > > > >> Hi David, > >> > >> On 6/11/26 21:43, David Laight wrote: > >>> On Thu, 11 Jun 2026 20:12:32 +0200 > >>> Ahmad Fatoum 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: That would certainly make 115200 a better default than 9600. David > > 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 > >>>> > >>>> > >>> > >>> > >> > >> > > > > >