PROCESSOR-SDK-AM65X: GPIO LEDs in device tree

Scott Whitney

Hi forum,

I'm feeling really dumb and need some help. We have two LEDs, a yellow one connected to GPIO1_28 and a red one connected to GPIO1_43. The LEDs are active high, i.e. they will turn on when the corresponding GPIO line is active high.

We'd like to control them using the "gpio-leds" driver, but having trouble figuring out the correct syntax in the device tree.

Within &main_pmx0, I can define a group of LED pins like:

    led_pins_default: led-pins-default {
        pinctrl-single,pins = <
            AM65X_IOPAD(0x01f0, PIN_OUTPUT, 7)    /* (AD11) GPIO1_28 (LED D2 - Yellow) */
            AM65X_IOPAD(0x022C, PIN_OUTPUT, 7)    /* (AD26) GPIO1_43 (LED D3 - Red) */
        >;

};

However, I cannot figure out the correct device tree syntax to enable these pins as individual LEDs so that they could be controlled via /sys/class/leds, or connected to kernel events.

Can anyone provide an example, perhaps with and without a kernel event?

Thanks, and apologies for not being able to figure this out from other examples. I think what is throwing me is that each GPIO port has a large number of pins on it, and that's not the case for most other processors.

Best regards!

Scott

over 6 years ago

0 Pavel Botev over 6 years ago

TI__Guru**** 170625 points

Hi Scott,

You can first explore how "gpio-keys" driver is implemented in AM65x DTS : k3-am654-base-board.dts, as for "gpio-leds" we have similar approach.

Then you can refer to below DTS files for exaple of "gpio-leds" driver coding in DTS:

linux-kernel/arch/arm/boot/dts/am57xx-beagle-x15-common.dtsi

linux-kernel/arch/arm/boot/dts/am437x-sk-evm.dts

linux-kernel/Documentation/devicetree/bindings/leds/leds-gpio.txt

Check also below e2e threads, these might be in help:

https://e2e.ti.com/support/processors/f/791/t/658992

https://e2e.ti.com/support/processors/f/791/t/826370

Regards,
Pavel

0 Scott Whitney over 6 years ago in reply to Pavel Botev

Expert 1120 points

Thanks for your help, Pavel,

For anyone trying the same sort of thing, this is what I ended up doing. In my DTS file, I had GPIO lines defined for the LEDs under &main_pmx0:

&main_pmx0 {

...

    main_gpio1_pins_default: main-gpio1-pins-default {
        pinctrl-single,pins = <
            /* LEDs */
            AM65X_IOPAD(0x01f0, PIN_OUTPUT, 7)    /* (AD11) GPIO1_28 (LED D2 - Yellow) */
            AM65X_IOPAD(0x022C, PIN_OUTPUT, 7)    /* (AD26) GPIO1_43 (LED D3 - Red) */
..etc...

At the top level of my DTS file, I then added:

/ {

...

    gpio-leds {
       compatible = "gpio-leds";

       led-yellow {
           gpios = <&main_gpio1 28 GPIO_ACTIVE_HIGH>;
           default-status = "off";
       };

       led-red {
           gpios = <&main_gpio1 43 GPIO_ACTIVE_HIGH>;
           default-state = "off";
       };
   };
};

After rebuilding Linux and writing it to an SD card, I was then able to test the LEDs using the sysfs interface, e.g.

cd /sys/class/leds/led-red

cat brightness

echo 1 > brightness # Turns on red LED

echo 0 > brightness # Turns off red LED

cat trigger

[none] kbd-scrolllock kbd-numlock kbd-capslock kbd-kanalock kbd-shiftlock kbd-al
tgrlock kbd-ctrllock kbd-altlock kbd-shiftllock kbd-shiftrlock kbd-ctrlllock kbd
-ctrlrlock disk-activity disk-read disk-write ide-disk heartbeat cpu cpu0 cpu1 c
pu2 cpu3 default-on panic mmc0 mmc1 rfkill-any rfkill-none

echo heartbeat > trigger # Flashing twice, delays, and repeats

echo mmc1 > trigger # Nothing happens

sync # Blinks once

echo none > trigger

You can do the same kinds of things using led-yellow, too.

Hope this helps - I appreciate the help from Pavel and hope this pays it forward a bit!

Scott

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PROCESSOR-SDK-AM65X: GPIO LEDs in device tree