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Date:   Fri, 28 Jul 2023 22:10:36 +0200
From:   =?utf-8?Q?Ond=C5=99ej?= Jirman <megi@xff.cz>
To:     Heiko Stuebner <heiko@sntech.de>
Cc:     Peter Geis <pgwipeout@gmail.com>,
        Javier Martinez Canillas <javierm@redhat.com>,
        linux-kernel@vger.kernel.org,
        Peter Robinson <pbrobinson@gmail.com>,
        Caleb Connolly <kc@postmarketos.org>,
        Jarrah Gosbell <kernel@undef.tools>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Martijn Braam <martijn@brixit.nl>,
        Rob Herring <robh+dt@kernel.org>,
        Tom Fitzhenry <tom@tom-fitzhenry.me.uk>,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-rockchip@lists.infradead.org
Subject: Re: [PATCH] arm64: dts: rockchip: Change serial baud rate for
 Pinephone Pro to 1.5 MB
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        Heiko Stuebner <heiko@sntech.de>, Peter Geis <pgwipeout@gmail.com>, 
        Javier Martinez Canillas <javierm@redhat.com>, linux-kernel@vger.kernel.org, 
        Peter Robinson <pbrobinson@gmail.com>, Caleb Connolly <kc@postmarketos.org>, 
        Jarrah Gosbell <kernel@undef.tools>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, 
        Martijn Braam <martijn@brixit.nl>, Rob Herring <robh+dt@kernel.org>, 
        Tom Fitzhenry <tom@tom-fitzhenry.me.uk>, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 
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Hi Heiko and Javier,

On Fri, Jul 28, 2023 at 08:59:50PM +0200, Heiko Stuebner wrote:
> 
> Hi Javier,
> 
> > Probably won't replace the DTB shipped with the firmware either? If one is
> > replacing the firmware provided DTB witch the one in the mainline kernel,
> > probably such person is also using mainline u-boot?
> 
> Not necessarily.
> 
> I.e. putting an extlinux.conf on an sd-card with a kernel-image and dtb
> is not rocket science ;-)
> 
> > For someone like me who is only using mainline u-boot, linux, etc then
> > having a consistent uart baud rate across all components is really useful.
> > 
> > Otherwise I either have serial console for u-boot or the kernel, but can't
> > have both working so is annoying.
> > 
> > It would be good to have a definite answer on this. Since every time that
> > I try to hack on my PPP, I end changing my DTS and remember this patch :)
> 
> So far people only reported "breaks my setup". I'm in a pickle here ;-) .
> Without anybody saying "I want to also move into this direction" I really
> feel I should not merge a patch that breaks other peoples setups.

Even if this is not changed in kernel, bootloader should fix this situation by
patching the kernel DTB before booting the kernel. U-Boot already patches the
DTB in several ways, so I guess it's possible to just change stdout-path either
in generic code, or in per-board ft_board_setup() for Pinephone Pro to something
that matches whatever the user configured via Kconfig:

https://elixir.bootlin.com/u-boot/latest/source/configs/pinephone-pro-rk3399_defconfig#L79

I mean that if U-Boot allows the user to configure arbitrary baudrate via
KConfig, then it *should* also update the kernel DTB to match, especially if the
choice is different from DTB that it actually embeds:

https://elixir.bootlin.com/u-boot/latest/source/arch/arm/dts/rk3399-pinephone-pro.dts#L29

No static baudrate choice in DT will save anyone anyway, with the provided flexibility
of configuration.

Maybe this would be a nice location to fix this:

https://elixir.bootlin.com/u-boot/v2023.07.02/source/common/fdt_support.c#L131

kind regards,
	o.

> 
> Heiko
> 
>