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

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Message-ID: <CAH+2xPBmWkb-m2S68SybAakJsFRizX-0T0YtXiHGFt+2Q=kpvA@mail.gmail.com>
Date: Thu, 2 Oct 2025 21:19:02 +0200
From: Bruno Thomsen <bruno.thomsen@...il.com>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>, Tony Lindgren <tony@...mide.com>, Judith Mendez <jm@...com>, 
	Kevin Hilman <khilman@...libre.com>, Arnd Bergmann <arnd@...db.de>, 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

Den tors. 2. okt. 2025 kl. 14.32 skrev Matti Vaittinen
<mazziesaccount@...il.com>:
>
> 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>

Reviewed-by: Bruno Thomsen <bruno.thomsen@...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