Messages in this thread | | | Subject | Re: [PATCH v5 0/6] bcm2835: auxiliar device support for spi | From | Phil Elwell <> | Date | Thu, 10 Sep 2015 18:02:47 +0100 |
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[ 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 = "brcm,bcm2835-aux-uart", "ns16550"; reg = <0x7e215040 0x40>; interrupts = <1 29>; clocks = <&clk_uart1>; reg-shift = <2>; no-loopback-test; status = "disabled"; }; };
clocks: clocks { ... clk_core: clock@2 { compatible = "fixed-clock"; reg = <2>; #clock-cells = <0>; clock-output-names = "core"; clock-frequency = <250000000>; }; ... clk_uart1: clock@6 { compatible = "fixed-factor-clock"; clocks = <&clk_core>; #clock-cells = <0>; clock-div = <1>; clock-mult = <2>; }; };
Phil
On 10/09/2015 16:57, Martin Sperl wrote: >> On 10.09.2015, at 17:48, Noralf Trønnes <noralf@tronnes.org> 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-139234607 >> >> 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… > > Martin
On 10/09/2015 16:57, Martin Sperl wrote: >> On 10.09.2015, at 17:48, Noralf Trønnes <noralf@tronnes.org> 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-139234607 >> >> 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… > > Martin
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