[AM335x] device tree leds{} and /sys/kernel/debug/gpio

Embedded Linux Discussions
1

Hi,
Custom board based upon BBB.
Kernel 5.11.10
snippets from my custom device tree

leds {
	pinctrl-names = "default";
	pinctrl-0 = <&user_leds_s0>;

	compatible = "gpio-leds";

	led1 {
		label = "zcpu:red:led"; /* ONBOARD RED LED */
		gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
		linux,default-trigger = "none";
		default-state = "off";
	};

	led2 {
		label = "zcpu:green:led"; /* ONBOARD GREEN LED */
		gpios = <&gpio0 9 GPIO_ACTIVE_HIGH>;
		linux,default-trigger = "none";
		default-state = "off";
	};

	led3 {
		label = "zcpu:blue:led"; /* ONBOARD BLUE LED */
		gpios = <&gpio0 11 GPIO_ACTIVE_HIGH>;
		linux,default-trigger = "heartbeat";
		default-state = "off";
	};
};

and

	user_leds_s0: user_leds_s0 {
		pinctrl-single,pins = <
			AM33XX_IOPAD(0x8d0, PIN_OUTPUT | MUX_MODE7)        /* (V2)  lcd_data12.gpio0[8]    (GPIO_8) ONBOARD RED LED*/
			AM33XX_IOPAD(0x8d4, PIN_OUTPUT | MUX_MODE7)        /* (V3)  lcd_data13.gpio1[9]    (GPIO_9) ONBOARD GREEN LED*/
			AM33XX_IOPAD(0x8dc, PIN_OUTPUT | MUX_MODE7)        /* (T5)  ldc_data15.gpio1[11]   (GPIO_11) ONBOARD BLUE LED*/
		>;
	};

The onboard leds work without a problem. They show up in /sys/class/leds.
ls /sys/class/leds
mmc0:: mmc1:: zcpu:blue:led zcpu:green:led zcpu:red:led

The RED led is GPIO0 pin 8.
The GREEN is GPIO0 pin 9.
The BLUE is GPIO0 pin 11.

Now I run this command,
cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 0-31, parent: platform/4804c000.gpio, gpio-0-31:
gpio-23 ( |sysfs ) out hi

gpiochip1: GPIOs 32-63, parent: platform/481ac000.gpio, gpio-32-63:
gpio-33 ( |sysfs ) out hi

gpiochip2: GPIOs 64-95, parent: platform/481ae000.gpio, gpio-64-95:

gpiochip3: GPIOs 96-127, parent: platform/44e07000.gpio, gpio-96-127:
gpio-104 ( |zcpu:red:led ) out lo
gpio-105 ( |zcpu:green:led ) out lo
gpio-107 ( |zcpu:blue:led ) out lo

I would expect the led(s) would show up under gpiochip0 pins 8, 9 and 11.
Now my question.
Why do the led(s) show up as pins under gpiochip3 pins 102, 104 and 107?

Thank you,

2

They were probed and put under control of the gpio-led driver at those locations.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/leds/leds-gpio.c?h=v6.1-rc3#n194

Regards,

3

RCN,
Referring to https://www.ti.com/lit/ug/spruh73q/spruh73q.pdf
Memory Map chapter
GPIO0 address start is 0x44E0_7000
GPIO1 0x4804_C000
GPIO2 0x481A_C000
GPIO3 0x481A_D000

The result of cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 0-31, parent: platform/4804c000.gpio, gpio-0-31:
gpiochip1: GPIOs 32-63, parent: platform/481ac000.gpio, gpio-32-63:
gpiochip2: GPIOs 64-95, parent: platform/481ae000.gpio, gpio-64-95:
gpiochip3: GPIOs 96-127, parent: platform/44e07000.gpio, gpio-96-127:

I was matching the addresses listed in the spruh with the platform/addresses reported by cat.
I noticed that the gpiochipx numbers are not aligned with the GPIOx number.
gpiochip0 = GPIO1
gpiochip1 = GPIO2
gpiochip2 = GPIO3
gpiochip3 = GPIO0

This misalignment explains a lot about why 0-31 exports to GPIO1 but there must be some history why the number are not aligned.
Why are they not aligned?

Thank you,

4

The kernel probes and loads them asynchronous… Thus in theory it should be more random, but usually always end up the same…

Regards,