Linkit Smart 7688 GPIO pin map on OpenWrt 21.02.0

For Developers
1

Hello

I'm trying to upgrade a bunch of devices based on Linkit Smart 7688 with the original installed version Chaos Calmer 15.05.1 to a newest version with Python 3 support.

My main problem has been the GPIO ports, I can't change them, because I need to keep the hardware backwards compatibility.

Linkit_Smart_7688
Linkit_Smart_76881767×876 204 KB

My first problem is in all the new versions I can't use the GPIO 12 and GPIO 13 because seems they are used by the UART 0. How can I disable the UART 0 or change it to a normal GPIO pins?

My second problem is when I tried with the version 18 and 19.07.8, I got the same GPIO pin map from the version 15 linked to the gpiochip0, gpiochip32 and gpiochip64.

2021-09-28_Linkit_gpio
2021-09-28_Linkit_gpio1157×210 6.74 KB

But when I tried version 21.02.0, I got GPIO ports with numbers over 400 linked to the gpiochip416, gpiochip448 and gpiochip480.

2021-09-28_Linkit_gpio-400
2021-09-28_Linkit_gpio-4001221×226 6.74 KB

I'm trying now to compile OpenWrt from the source code with all the packages that we need, but still I have problems with the GPIO pins. Where is the configuration file to maps the GPIO ports?

Thanks in advance
Jose

2

Hello joniuz,

Maybe you can disable uartlite (mapped to uart0 pins) in your LINKIT7688.dts:

		uartlite@c00 {
			status = "disabled";
		};

For example, at the top of uart1 and uart2 inside the palmbus statement:

		uartlite@c00 {
			status = "disabled";
		};

		uart1@d00 {
			status = "okay";
		};

		uart2@e00 {
			status = "okay";
		};

Maybe serial order in /dev/ttySx could change, so test and change the console in bootargs to the desired one.

Hope this works!

3

I had a similar situation where I was using uartlite pins as gpios.

Had the below configuration in my dts. Everything working, I could now use gpio#12 and gpio#13, uart2 (Used as Debug) mapped to ttyS0 and uart1 mapped to ttyS1.

#include "mt7628an.dtsi"

#include <dt-bindings/gpio/gpio.h>
#include <dt-bindings/input/input.h>

/ {
........
........
	chosen {
		bootargs = "console=ttyS0,57600";	/* Changed from ttyS2 since uart2 is configured to appear as ttyS0  in "aliases" node */
	};

	aliases {
		serial0 = &uart2;	/* Force uart2 to appear as ttyS0 */
		serial1 = &uart1;	/* Force uart1 to appear as ttyS1 */
	};
......
......
&state_default {
..............
	uartlite {
		groups = "uart0";
		function = "gpio";
	};
};

....
&uartlite {
	status = "disabled";
};

The above was implemented in openwrt 21.02

Afterwards, if you export gpio 492 and 493 below will be match
gpio#12 -> gpio-492
gpio#13 -> gpio-493

You can view the gpio configuration with:

root@mylinkit:/# cat /sys/kernel/debug/gpio
gpiochip2: GPIOs 416-447, parent: platform/10000600.gpio, 10000600.gpio-bank2:
.....
gpiochip1: GPIOs 448-479, parent: platform/10000600.gpio, 10000600.gpio-bank1:
.....
gpiochip0: GPIOs 480-511, parent: platform/10000600.gpio, 10000600.gpio-bank0:
gpio-492 (                    |sysfs             ) in  hi
gpio-493 (                    |sysfs             ) in  hi

Hope this helps