From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Elwell Subject: Re: [PATCH v5 0/6] bcm2835: auxiliar device support for spi Date: Thu, 10 Sep 2015 18:02:47 +0100 Message-ID: <55F1B7B7.3050604@raspberrypi.org> References: <1441359711-2800-1-git-send-email-kernel@martin.sperl.org> <87h9n4weg8.fsf@eliezer.anholt.net> <55F1A651.5090102@tronnes.org> <8B777380-A2A1-475E-8A1C-942BF28EE160@martin.sperl.org> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <8B777380-A2A1-475E-8A1C-942BF28EE160@martin.sperl.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Martin Sperl , =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= Cc: Mark Rutland , devicetree@vger.kernel.org, Ian Campbell , Russell King , Pawel Moll , Stephen Warren , Lee Jones , linux-kernel@vger.kernel.org, Rob Herring , linux-spi@vger.kernel.org, Eric Anholt , Mark Brown , linux-rpi-kernel@lists.infradead.org, Kumar Gala , linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org [ Sending again in plain text ] Noralf pointed me at fixed-factor-clock, and that works in our (downstream) environment: soc: soc { ... uart1: uart@7e215040 { compatible =3D "brcm,bcm2835-aux-uart", "ns16550"; reg =3D <0x7e215040 0x40>; interrupts =3D <1 29>; clocks =3D <&clk_uart1>; reg-shift =3D <2>; no-loopback-test; status =3D "disabled"; }; }; clocks: clocks { ... clk_core: clock@2 { compatible =3D "fixed-clock"; reg =3D <2>; #clock-cells =3D <0>; clock-output-names =3D "core"; clock-frequency =3D <250000000>; }; ... clk_uart1: clock@6 { compatible =3D "fixed-factor-clock"; clocks =3D <&clk_core>; #clock-cells =3D <0>; clock-div =3D <1>; clock-mult =3D <2>; }; }; Phil On 10/09/2015 16:57, Martin Sperl wrote: >> On 10.09.2015, at 17:48, Noralf Tr=F8nnes wrote: >> >> This looks interesting. >> But there's a challenge with the uart1 and the 8250 driver. >> >> Phil Elwell has this to say: >> This means that that UART1 isn't an exact clone of a 8250 UART. >> In a particular, the clock divisor is calculated differently. >> A standard 8250 derives the baud rate as clock/(divisor16), >> whereas the BCM2835 mini UART uses clock/(divisor8). This means >> that if you want to use the standard driver then you need to lie >> about the clock frequency, providing a value is twice the real >> value, in order for a suitable divisor to be calculated. >> >> Ref: https://github.com/raspberrypi/linux/pull/1008#issuecomment-1392346= 07 >> >> So either we need a new uart1 driver or a doubled clock freq. somehow. > Found out the same thing and communicated it to Eric - not = > knowing about the different divider=85 > > Martin On 10/09/2015 16:57, Martin Sperl wrote: >> On 10.09.2015, at 17:48, Noralf Tr=F8nnes wrote: >> >> This looks interesting. >> But there's a challenge with the uart1 and the 8250 driver. >> >> Phil Elwell has this to say: >> This means that that UART1 isn't an exact clone of a 8250 UART. >> In a particular, the clock divisor is calculated differently. >> A standard 8250 derives the baud rate as clock/(divisor16), >> whereas the BCM2835 mini UART uses clock/(divisor8). This means >> that if you want to use the standard driver then you need to lie >> about the clock frequency, providing a value is twice the real >> value, in order for a suitable divisor to be calculated. >> >> Ref: https://github.com/raspberrypi/linux/pull/1008#issuecomment-1392346= 07 >> >> So either we need a new uart1 driver or a doubled clock freq. somehow. > Found out the same thing and communicated it to Eric - not = > knowing about the different divider=85 > > Martin