Struggling with PWM [sysfs interface] STM32MP157F

[FFont.1]

Hello,

I'm trying to PWM some pins using the sysfs interface on the openSTLinux but unfortunately, it's not working.

I've been changing the device tree files in order to get it working, but still without success.

I'm trying to follow this wiki but when I run the:

ls /sys/class/pwm

I get nothing.

What could be the issue? PWM is enabled on the kernel.

I've attached the modified device tree files.

Best regards,

Fernando Fontes

[Kevin HUBER]

Hello @FFont.1​ ,

Please can you indicates to us which linux version are you using?

Is it the one from the Developer Package?

Is it a custom one from Yocto Distribution Package?

Regarding your problem, can you see the other folders inside /sys/class?

ls /sys/class

Regards,

Kevin

[FFont.1]

Hello @Kevin HUBER​ ,

Linux version, from Distribution Package:

root@stm32mp1:~# uname -a
Linux stm32mp1 5.4.56 #1 SMP PREEMPT Wed Jan 5 11:56:19 WET 2022 armv7l armv7l armv7l GNU/Linux

And yes, I can see other folders:

root@stm32mp1:~# ls  /sys/class
ata_device  block	 dma	   i2c-adapter	mdio_bus  net  regulator    scsi_disk	  spidev   typec_mux  vtconsole
ata_link    bluetooth	 drm	   i2c-dev	mem	  phy  remoteproc   scsi_generic  tee	   ubi	      wakeup
ata_port    bsg		 extcon    ieee80211	misc	  pps  rfkill	    scsi_host	  thermal  udc	      watchdog
backlight   devcoredump  graphics  input	mmc_host  ptp  rtc	    sound	  tty	   usb_role
bdi	    devfreq	 hwmon	   leds		mtd	  pwm  scsi_device  spi_master	  typec    vc

Thank you for the ongoing support.

Best regards,

Fernando

[Kevin HUBER · Accepted solution]

Hi @FFont.1​ ,

Ok thank you, I thought that you did not have the entire folder pwm.

To have the folder pwmchipx inside the folder /sys/class/pwm, you have to configure and enable a timer in your dts.

In this timer, you must define a child node pwm and set its pins.

https://wiki.st.com/stm32mpu/wiki/TIM_device_tree_configuration#DT_configuration

I looked at the DTS that you sent and I have the impression that you enabled timers1 for that purpose:

&timers1 {
	/* spare dmas for other usage */
	/delete-property/dmas;
	/delete-property/dma-names;
	status = "okay";
	pwm1: pwm {
		pinctrl-0 = <&pwm1_pins_a>;
		pinctrl-1 = <&pwm1_sleep_pins_a>;
		pinctrl-names = "default", "sleep";
		status = "okay";
	};
	timer@0 {
		status = "okay";
	};
};

You have set the pwm pinctrl to pins a.

But your pinctrl settings in stm32mp15-pinctrl.dtsi are weird:

	pwm1_pins_a: pwm1-0 {
		pins {
			pinmux = <STM32_PINMUX('A', 15, AF1)>,
				 <STM32_PINMUX('H', 6, AF1)>;
			bias-pull-down;
			drive-push-pull;
			slew-rate = <0>;
		};
	};
 
	pwm1_sleep_pins_a: pwm1-sleep-0 {
		pins {
			pinmux = <STM32_PINMUX('A', 15, ANALOG)>,
				<STM32_PINMUX('H', 6, ANALOG)>;
		};
	};

If you look at the datasheet of the STM32MP157F, page 94: https://www.st.com/resource/en/datasheet/stm32mp157c.pdf

PA15 AF1 is not related to timers 1, but to TIM2

and

PH6 AF1 is not existing:

 

So it can't work.

I tested on my 157F-DK2 and as an example, I succeeded to have the content of /sys/class/pwm/ by configuring the timers8.

Since on my board the pin PC7 is available, I added a pwm pinmux into my pinctrl "stm32mp15-pinctrl.dtsi" :

	pwm8_pins_b: pwm8-1 {
		pins {
			pinmux = <STM32_PINMUX('C', 7, AF3)>; /* TIM8_CH2 */
			bias-pull-down;
			drive-push-pull;
			slew-rate = <0>;
		};
	};
 
	pwm8_sleep_pins_b: pwm8-sleep-1 {
		pins {
			pinmux = <STM32_PINMUX('C', 7, ANALOG)>; /* TIM8_CH2 */
		};
	};

Because PC7 AF3 is dedicated to TIM8:

Then I configured the timers8 in stm32mp157f-dk2.dts to use these pins in its subnode pwm:

&timers8 {
	status = "okay";
	dmas = <&dmamux1 47 0x400 0x80000001>;
	dma-names = "ch1";
	pwm {
		pinctrl-0 = <&pwm8_pins_b>;
		pinctrl-1 = <&pwm8_sleep_pins_b>;
		pinctrl-names = "default", "sleep";
		status = "okay";
	};
};

Once you are on the board, you can check if the pin is well claimed by viewing the content of:

cat /sys/kernel/debug/pinctrl/soc\:pin-controller@50002000/pinmux-pins | grep "timer"

It gives me:

pin 39 (PC7): device 44001000.timer:pwm function af3 group PC7

Which confirms that it worked.

Now you can verify the content of your folder:

root@stm32mp1:~# ls /sys/class/pwm/
pwmchip0
root@stm32mp1:~# ls /sys/class/pwm/pwmchip0/
device  export  npwm  power  subsystem  uevent  unexport

Done!

Hope it helps you,

Regards,

Kevin

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[FFont.1]

Hello Kevin,

Yes, you are right! I was doing it wrong.

I've managed to put it to work thanks to you.

I've only one last question regarding the PH6 pin.

 

I suppose it's possible to use TIM12_CH1 to PWM the pin? Or am I wrong?

Best regards,

Fernando

[Kevin HUBER]

Hello @FFont.1​ ,

Yes, you can use the pin PH6 to use TIM12_CH1 with the PWM.

But if you choose to use this pin, you have to use the timers12 (TIM12)

and specify that you want to use the alternate function 2 (columns AF2 of the array)

<STM32_PINMUX('H', 6, AF2)>; /*TIM12_CH1*/

You also have to be careful and verify that the pin PH6 is available and not already used by someone.

Regards,

Kevin

In order to give better visibility on the answered topics, please click on 'Select as Best' on the reply which solved your issue or answered your question. See also 'Best Answers'

[FFont.1]

Hello Kevin,

Thank you very much for the reply.

That was it. Another program was using the PH6. Therefore, on my first attempt to PWM the pin, it wasn't working at all.

Best regards,

Fernando Fontes