linux-kernel - Re: [PATCH] ARM: dts: am33xx: Add missing serial console speed

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Message-ID: <609ec2e6-c877-4fc5-95b7-935ae2549b3a@gmail.com>
Date: Thu, 2 Oct 2025 15:32:53 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Geert Uytterhoeven <geert+renesas@...der.be>,
 Tony Lindgren <tony@...mide.com>, Bruno Thomsen <bruno.thomsen@...il.com>,
 Judith Mendez <jm@...com>, Kevin Hilman <khilman@...libre.com>,
 Arnd Bergmann <arnd@...db.de>
Cc: linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: am33xx: Add missing serial console speed

On 02/10/2025 12:53, Geert Uytterhoeven wrote:
> Without a serial console speed specified in chosen/stdout-path in the
> DTB, the serial console uses the default speed of the serial driver,
> unless explicitly overridden in a legacy console= kernel command-line
> parameter.
> 
> After dropping "ti,omap3-uart" from the list of compatible values in DT,
> AM33xx serial ports can no longer be used with the legacy OMAP serial
> driver, but only with the OMAP-flavored 8250 serial driver (which is
> mutually-exclusive with the former).  However, replacing
> CONFIG_SERIAL_OMAP=y by CONFIG_SERIAL_8250_OMAP=y (with/without enabling
> CONFIG_SERIAL_8250_OMAP_TTYO_FIXUP) may not be sufficient to restore
> serial console functionality: the legacy OMAP serial driver defaults to
> 115200 bps, while the 8250 serial driver defaults to 9600 bps, causing
> no visible output on the serial console when no appropriate console=
> kernel command-line parameter is specified.
> 
> Fix this for all AM33xx boards by adding ":115200n8" to
> chosen/stdout-path.  This requires replacing the "&uartN" reference by
> the corresponding "serialN" DT alias.
> 
> Fixes: ca8be8fc2c306efb ("ARM: dts: am33xx-l4: fix UART compatible")
> Fixes: 077e1cde78c3f904 ("ARM: omap2plus_defconfig: Enable 8250_OMAP")
> Closes: https://lore.kernel.org/CAMuHMdUb7Jb2=GqK3=Rn+Gv5G9KogcQieqDvjDCkJA4zyX4VcA@mail.gmail.com
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Reviewed-by: Matti Vaittinen <mazziesaccount@...il.com>
Tested-by: Matti Vaittinen <mazziesaccount@...il.com>

(Tested booting on Beaglebone black with a config and kernel command 
line which were NOT affected by the issue. Well, prints do still get 
through the UART to my minicom, so things seem to work for me after this 
change as well :) )

The change does also look Ok to me.

Yours,
	-- Matti