i.MX6: Using GPIO1_IO19

[lynix]

My intent is to configure the WDOG1 pin on the i.MX6 as GPIO output (to trigger a custom power-off circuit). The i.MX6 Reference Manual states that this is achievable by setting the Pad Mux Register (IOMUXC_SW_MUX_CTL_PAD_SD1_DATA2) MUX_MODE to ALT5, which selects the signal GPIO1_IO19.

In order to implement this, I have added the following lines to the iomuxc-block in the Linux Kernel device tree:

gpio19 {

    pinctrl_gpio19_1: gpio19grp-1 {

        fsl,pins = <

            MX6QDL_PAD_SD1_DAT2__GPIO1_IO19 0x80000000

        >;

    }; 

};

From userspace I am now able to configure and use the GPIO like this:

$ echo 19 > /sys/class/gpio/export

$ echo out > /sys/class/gpio/gpio19/direction

$ echo 1 > /sys/class/gpio/gpio19/active_low

$ echo 1 > /sys/class/gpio/gpio19/value

(unfortunately I don't have a scope so I can't verify that the output value actually changes)

My question now is how to do this initialization in the device tree, so that I have the GPIO properly set up on system boot without using userland scripts?

My understanding is that I'd have to create a "gpio19" device in the tree that makes use of the pinctrl block I have defined, but I don't know how to declare such a device. This document describes properties for such a device that I don't know which values I'd have to assign to, e.g. the interrupt number.

I'm using a TQMa6S board with the latest BSP 0105.

Thanks in advance for any feedback! :smileyhappy:

[BiyongSUN]

Please check the base and lable to indetify the number of gpio in linux.

GPIO1_19 should be the GPIO1 base + 19.

for example:

root@imx6qdlsolo:~# cat /sys/class/gpio/gpiochip32/base

32

root@imx6qdlsolo:~# cat /sys/class/gpio/gpiochip32/label

20a0000.gpio

[lynix]

Thank you for the hint; I was naive and assumed it to be 19.

Check according your hint confirmed that:

  root@MBa6x:~ cat /sys/class/gpio/gpiochip0/base

0

(There is no /sys/class/gpio/gpiochip1, I think they are just indexed by 0)

[BiyongSUN]

what is the lable?

It is the value to indentify the gpio, which is in the device tree.

In that way, you can figure out which is the base for.

[frankba · Accepted solution]

Hi Alexander,

not sure if I got your question right. A common trick is to use the GPIO as a LED. In the device tree, insert a block like:

/ {

...

    leds {

        compatible = "gpio-leds";

        my_led {

            gpios = <&gpio1 19 GPIO_ACTIVE_LOW>;

        };
    };
...

which will automatically create a LED that can be switched on and off:

echo 1 >  /sys/class/leds/my_led/brightness

echo 0 >  /sys/class/leds/my_led/brightness

Frank

[lynix]

Exactly what I was looking for, thanks! :smileyhappy: