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References: <20230403175937.2842085-1-javierm@redhat.com> <3738011.44csPzL39Z@diego>
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From:   Peter Geis <pgwipeout@gmail.com>
Date:   Tue, 4 Apr 2023 08:52:02 -0400
Message-ID: <CAMdYzYqT=vVZxFK=P6xYDAht_KWk3CTsTtruPAbGqx1K9EcJsQ@mail.gmail.com>
Subject: Re: [PATCH] arm64: dts: rockchip: Change serial baud rate for
 Pinephone Pro to 1.5 MB
To:     =?UTF-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>
Cc:     linux-kernel@vger.kernel.org,
        Javier Martinez Canillas <javierm@redhat.com>,
        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>, Ondrej Jirman <megi@xff.cz>,
        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
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On Tue, Apr 4, 2023 at 3:55=E2=80=AFAM Heiko St=C3=BCbner <heiko@sntech.de>=
 wrote:
>
> Hi,
>
> Am Montag, 3. April 2023, 19:59:37 CEST schrieb Javier Martinez Canillas:
> > This baud rate is set for the device by mainline u-boot and is also wha=
t
> > is set in the Pinebook Pro Device Tree, which is a device similar to th=
e
> > PinePhone Pro but with a different form factor.
> >
> > Otherwise, the baud rate of the firmware and Linux don't match by defau=
lt
> > and a 'console=3DttyS2,1500000n8' kernel command line parameter is requ=
ired
> > to have proper output for both.
>
> The interesting question is always if this will break someone else's setu=
p.
> I've never really understood the strange setting of 1.5MBps, but on the
> other hand it _is_ a reality on most boards.

Good Morning Heiko,

The 1.5M baud is default because the clock structure on rockchip
devices does not allow a clean 115200 baud. By attempting to force
115200, it will always be slightly off (either low or high depending
on how the driver decided to round). If this actually causes any
problems is the subject of much debate.

Very Respectfully,
Peter Geis

>
> Personally I don't care that much either way, but would like a comment
> from the other people working on that device - if possible.
>
> I guess if we don't hear anything, I'll apply it nevertheless at some poi=
nt
>
>
> Heiko
>
>
> > Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> > ---
> >
> > I tried to instead get rid of the baud rate altogether, as suggested by
> > Peter Robinson. AFAIU that should just pick whatever bad rate has been
> > using by the early console.
> >
> > But neither using 'stdout-path =3D "serial2" nor 'stdout-path =3D &uart=
2'
> > worked for me.
> >
> > In both cases I didn't have any output unless setting a baud rate using
> > the 'console=3D'param.
> >
> >  arch/arm64/boot/dts/rockchip/rk3399-pinephone-pro.dts | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/boot/dts/rockchip/rk3399-pinephone-pro.dts b/ar=
ch/arm64/boot/dts/rockchip/rk3399-pinephone-pro.dts
> > index a0795a2b1cb1..6bbe65bd5bd4 100644
> > --- a/arch/arm64/boot/dts/rockchip/rk3399-pinephone-pro.dts
> > +++ b/arch/arm64/boot/dts/rockchip/rk3399-pinephone-pro.dts
> > @@ -26,7 +26,7 @@ aliases {
> >       };
> >
> >       chosen {
> > -             stdout-path =3D "serial2:115200n8";
> > +             stdout-path =3D "serial2:1500000n8";
> >       };
> >
> >       gpio-keys {
> >
> > base-commit: 3adf89324a2b2a9dbc2c12d8895021e7e34e3346
> >
>
>
>
>
>
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