MYS-6ULX-IOT modified device trees

In this repository I share modified device tree from the preconfigured Linux source provided by MYIR Tech for the MYS-6ULX-IOT iMX6ULL based board to enable the SPI bus in order to use userspace SPIDEV under /dev/spidev0.*. I also disable some unnecessary stuff i don't use.

Prerequisites

1. Preconfigured Linux source: available SDK provided by MYIR Tech under https://d.myirtech.com/MYS-6ULX/ - Sources
2. SPI related linux drivers: spi plattform related drivers for the IMX6 soc and spidev related stuff should be enabled within menuconfig and compiled as a module or built-in

Compiling DTS

1. Navigate to the linux source root directory
2. Under the terminal run to preprocess the DTS:

    cpp -nostdinc -I include -I arch  -undef -x assembler-with-cpp arch/arm/boot/dts mys-6ull-14x14-gpmi-weim.dts mys-6ull-14x14-gpmi-weim.dts.preprocessed

3. Run to get the device tree blob:

    dtc -I dts -O dtb -p 0x1000 mys-6ull-14x14-gpmi-weim.dts.preprocessed -o mys-6ull-14x14-gpmi-weim-modified.dtb

Updating DTB under U-BOOT

1. Copy the modified DTB into the boot partition (in my config I boot from sdcard and the bootloader is running from the nand flash)
2. Set DTB environment variable, base address and load it to the bootloader:

    setenv fdt_file mys-6ull-14x14-gpmi-weim-modified.dtb
    setenv fdt_addr_r 0x83000000     
    load mmc 0:1 ${fdt_addr_r} ${fdt_file}

3. If you don't want to change anything else save u-boot configuration and you can boot:

    saveenv
    boot

4. Complete reconfiguration of the bootloader:

    setenv fdt_file mys-6ull-14x14-gpmi-weim-modified.dtb 
    setenv fdt_addr_r 0x83000000     
    load mmc 0:1 ${fdt_addr_r} ${fdt_file}


    load mmc 0:1 ${loadaddr} zImage

    bootz ${loadaddr} - ${fdt_addr_r}

    setenv bootcmd 'load mmc 0:1 ${loadaddr} zImage; load mmc 0:1 ${fdt_addr_r} ${fdt_file}; bootz ${loadaddr} - ${fdt_addr_r}'

    saveenv

Enabling SPI bus

• Setting 2 chipselect pins
• compatible is set to "rohm,dh2228fv" instead of "spidev" so there is no stack trace error at boot (dmesg)
• pin cs set to active logic 0 - as typical too

    &ecspi1 {
        fsl,spi-num-chipselects = <2>;
        cs-gpios = <&gpio4 26 0>, <&gpio4 24 0>; 
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_ecspi1 &pinctrl_ecspi1_cs>;
        status = "okay";

        spidev@0 {
            compatible = "rohm,dh2228fv";
            spi-max-frequency = <8000000>;
            reg = <0>;
        };

        spidev@1 {
            compatible = "rohm,dh2228fv";
            spi-max-frequency = <8000000>;
            reg = <1>;
        };
    };

Assigning pins

    pinctrl_ecspi1: ecspi1grp {
		fsl,pins = <
			MX6UL_PAD_CSI_DATA07__ECSPI1_MISO 0x100b1
			MX6UL_PAD_CSI_DATA06__ECSPI1_MOSI 0x100b1
			MX6UL_PAD_CSI_DATA04__ECSPI1_SCLK 0x100b1
		>;
	};
	
	pinctrl_ecspi1_cs: ecspi1cs {
		fsl,pins = <
			MX6UL_PAD_CSI_DATA05__GPIO4_IO26 0x80000000 //CS0
			MX6UL_PAD_CSI_DATA03__GPIO4_IO24 0x80000000 //CS1
		>;
	};

Resources

Resolve stack trace: https://yurovsky.github.io/2016/10/07/spidev-linux-devices.html

Resolve dts compilation error with typical command: https://stackoverflow.com/questions/50658326/device-tree-compiler-not-recognizes-c-syntax-for-include-files

Disclaimer

All other necessary files for the board were supplied by MYIR Tech SDK and I share the modification to be available as a resource. Wish i had that when i did it.

Use it at your own responsibility.

If any mistakes let me know.