dtoverlay=i2c-gpio for Le Potato?

pmarks

I'm using i2c to talk to a sensor, but another peripheral is blocking the primary i2c pins.  On my RPi3B+, I added this line to /boot/config.txt, which defines /dev/i2c-6 using the pins I want:

    dtoverlay=i2c-gpio,bus=6,i2c_gpio_scl=9,i2c_gpio_sda=10

How can I port this configuration to Le Potato?  `ldto enable i2c-b` sort-of works, but it hard-codes pins 27-28. I want to share the same pinout between RPi and LePotato, and everyone says to avoid pins 27-28 on RPi: "i2c-0 is NOT available for use from the ARM on Pi3. Bad things will happen if you try."

For reference, my code is at https://github.com/pmarks-net/exhale

pmarks

I found a solution, but everything is hard-coded because I can't pass parameters to the overlay:

$ cat exhale/lepotato/i2c-exhale.dts
/*
Trying to emulate this RasPi config:
 dtoverlay=i2c-gpio,bus=6,i2c_gpio_scl=9,i2c_gpio_sda=10

The bus=6 feature is RasPi-exclusive, so we'll have to discover the
correct bus number from /sys/devices/platform/i2c-exhale/i2c-*

How to install this:

git clone https://github.com/libre-computer-project/libretech-wiring-tool
cp -v exhale/lepotato/i2c-exhale.dts libretech-wiring-tool/libre-computer/aml-s905x-cc/dt/
cd libretech-wiring-tool
make
sudo ./ldto enable i2c-exhale  # enable immediately
sudo ./ldto merge i2c-exhale   # enable on boot
*/

/dts-v1/;
/plugin/;

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

/ {
   fragment@0 {
       target-path = "/";

       __overlay__ {
           i2c_gpio: i2c-exhale {
               compatible = "i2c-gpio";
               /* Pin numbers from "lgpio header 7J1", Line column. */
               gpios = <&gpio 87 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN) /* sda GPIOX_8 */
                    &gpio 88 (GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN) /* scl GPIOX 9 */
                   >;
               /* SCL frequency is (500 / udelay) kHz */
               i2c-gpio,delay-us = <10>;  /* ~50 kHz */
               #address-cells = <1>;
               #size-cells = <0>;
           };
       };
   };
};