[PATCH] ARM: dts: bcm2837-rpi-3-b: fix pwm1 pin

[Eric Anholt]

Stefan Wahren <stefan.wahren at i2se.com> writes:

> Hi Baruch,
>
>> Baruch Siach <baruch at tkos.co.il> hat am 31. Dezember 2017 um 16:12 geschrieben:
>> 
>> 
>> Raspberry Pi 3 uses GPIO45 for I2C SCL0. pwm1 is on GPIO41. Update the
>> DT description accordingly. Fix the following error that shows when
>> GPIO44 and GPIO45 are configured to I2C:
>> 
>> [    1.751563] pinctrl-bcm2835 3f200000.gpio: pin gpio45 already requested by 3f205000.i2c; cannot claim for 3f20c000.pwm
>> [    1.762474] pinctrl-bcm2835 3f200000.gpio: pin-45 (3f20c000.pwm) status -22
>> [    1.775176] pinctrl-bcm2835 3f200000.gpio: could not request pin 45 (gpio45) from group gpio45  on device pinctrl-bcm2835
>> [    1.786344] bcm2835-pwm 3f20c000.pwm: Error applying setting, reverse things back
>> [    1.793980] bcm2835-pwm: probe of 3f20c000.pwm failed with error -22
>> 
>> Signed-off-by: Baruch Siach <baruch at tkos.co.il>
>> ---
>>  arch/arm/boot/dts/bcm2837-rpi-3-b.dts | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/arch/arm/boot/dts/bcm2837-rpi-3-b.dts b/arch/arm/boot/dts/bcm2837-rpi-3-b.dts
>> index a8844d033b3f..b44b3b5af00d 100644
>> --- a/arch/arm/boot/dts/bcm2837-rpi-3-b.dts
>> +++ b/arch/arm/boot/dts/bcm2837-rpi-3-b.dts
   >> @@ -60,3 +60,9 @@
>>  	status = "okay";
>>  	bus-width = <4>;
>>  };
>> +
>> +&pwm {
>> +	pinctrl-names = "default";
>> +	pinctrl-0 = <&pwm0_gpio40 &pwm1_gpio41>;
>> +	status = "okay";
>> +};
>
> thanks for addressing this old issue. Unfortunately this is only a part of the solution. The real problem is the definition of pinctrl in a very common dtsi file (bcm2835-rpi.dtsi). Based on the Firmware dt-blob i created a pin usage map [1], which also shows a potential conflict on RPI Zero W.
>
> So i think we should remove the pwm part from bcm2835-rpi.dtsi and define it on board level like in your patch, but also for the other boards. My suggestion would be the following (based on Firmware):
>
> A Plus -> PWM on pin 40,45
> A -> PWM on pin 40,45
> B Plus -> PWM on pin 40,45
> B Rev 2 -> PWM on pin 40,45
> B -> PWM on pin 40,45
> 2 b -> PWM on pin 40,45
> 3 b -> PWM on pin 40,41
> Zero -> No PWM
> Zero W -> No PWM
>
> But i think we should wait for Eric's opinion.

This seems like a reasonable plan for resolving the boot error. The
alternative I can see would be to drop our pwm pinmux setup, in the
absence of any consumer of pwm trying to use it for some specific
purpose.

(Some day it would be nice to have an analog audio driver using pwm on
these pins, but I'm not volunteering to write that code either)
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