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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id u15-20020a05600c19cf00b003ede3f5c81fsm18542538wmq.41.2023.04.18.05.11.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Apr 2023 05:11:54 -0700 (PDT) From: Javier Martinez Canillas To: Heiko =?utf-8?Q?St=C3=BCbner?= , Peter Geis Cc: linux-kernel@vger.kernel.org, Peter Robinson , Caleb Connolly , Jarrah Gosbell , Krzysztof Kozlowski , Martijn Braam , Ondrej Jirman , Rob Herring , Tom Fitzhenry , 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 In-Reply-To: <3999080.iIbC2pHGDl@diego> References: <20230403175937.2842085-1-javierm@redhat.com> <3738011.44csPzL39Z@diego> <3999080.iIbC2pHGDl@diego> Date: Tue, 18 Apr 2023 14:11:53 +0200 Message-ID: <87h6tdie46.fsf@minerva.mail-host-address-is-not-set> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Heiko St=C3=BCbner 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=E2=80=AFAM Heiko St=C3=BCbner wrote: >> > >> > Hi, >> > >> > Am Montag, 3. April 2023, 19:59:37 CEST schrieb Javier Martinez Canill= as: >> > > 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 de= fault >> > > and a 'console=3DttyS2,1500000n8' kernel command line parameter is r= equired >> > > to have proper output for both. >> > >> > The interesting question is always if this will break someone else's s= etup. >> > 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 ? --=20 Best regards, Javier Martinez Canillas Core Platforms Red Hat