linux-kernel - Re: [PATCH] arm64: dts: rockchip: Change serial baud rate for Pinephone Pro to 1.5 MB

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Message-ID: <3797122.KgjxqYA5nG@diego>
Date:   Tue, 18 Apr 2023 16:26:23 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Peter Geis <pgwipeout@...il.com>,
        Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Robinson <pbrobinson@...il.com>,
        Caleb Connolly <kc@...tmarketos.org>,
        Jarrah Gosbell <kernel@...ef.tools>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Martijn Braam <martijn@...xit.nl>, Ondrej Jirman <megi@....cz>,
        Rob Herring <robh+dt@...nel.org>,
        Tom Fitzhenry <tom@...-fitzhenry.me.uk>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] arm64: dts: rockchip: Change serial baud rate for Pinephone Pro
 to 1.5 MB

Hi,

Am Dienstag, 18. April 2023, 14:11:53 CEST schrieb Javier Martinez Canillas:
> Heiko Stübner <heiko@...ech.de> writes:
> 
> Hello Heiko,
> 
> > Hi Peter,
> >
> > Am Dienstag, 4. April 2023, 14:52:02 CEST schrieb Peter Geis:
> >> On Tue, Apr 4, 2023 at 3:55 AM Heiko Stübner <heiko@...ech.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 what
> >> > > is set in the Pinebook Pro Device Tree, which is a device similar to the
> >> > > PinePhone Pro but with a different form factor.
> >> > >
> >> > > Otherwise, the baud rate of the firmware and Linux don't match by default
> >> > > and a 'console=ttyS2,1500000n8' kernel command line parameter is required
> >> > > to have proper output for both.
> >> >
> >> > The interesting question is always if this will break someone else's setup.
> >> > I've never really understood the strange setting of 1.5MBps, but on the
> >> > other hand it _is_ a reality on most boards.
> >
> >> 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.
> >
> > thanks so much for this piece of clock-detail. As I wrote, I never really
> > understood the why _before_ but also never cared that much to dive
> > into it and find out.
> >
> > So your explanation closes one knowledge gap in my head.
> >
> > Thanks a lot :-)
> 
> Did you make a decision about this? I guess the clock explanation is yet
> another argument in favour of switching the PPP to a 1.5 Mbps baud rate ?

Sorry, but no decision made here. Either way it's breaking for someone,
which makes this quite hard.

The rate accuracy is the one side, the two-boot issue is the other side.
And mainline u-boot (and levinboot - whatever that is) provides a 3rd side.

People starting with the phone probably won't replace the bootloader
in a first step but instead might play with a system image or newer kernel.
So if the uart will break for everyone using the default bootloader from
the factory that is somewhat bad.

I don't have a Pinephone Pro myself, so I really hoped for some Acks
or similar to appear in the meantime.

Do we have someone with an actual Pine64 affiliation in this loop?


Heiko