OrangePI Zero overlay and uboot/armbian

The Armbian has good documentation about how to use device overlays for their uboot scripts.  I wanted to dive a little deeper and understand some of the basics and still use buildroot.

Boot process of uboot, there is a file on the FAT partition boot.src, this is a binary file generated by mkimage.  The source file is in board/orangepi/orangepi-zero boot.sh:
setenv fdt_high ffffffff
setenv load_addr "0x44000000"
echo "Boot script loaded from ${devtype}"

setenv bootargs console=ttyS0,115200 earlyprintk root=/dev/mmcblk0p2 rootwait

fatload mmc 0 $kernel_addr_r zImage
fatload mmc 0 $fdt_addr_r sun8i-h2-plus-orangepi-zero.dtb
fdt addr ${fdt_addr_r}
fdt resize 65536
setenv processorName sun8i-h3-
setenv overlays i2c0  spi-spidev
for overlay_file in ${overlays}; do
    echo " looking for  ${processorName}${overlay_file}.dtbo"
    if fatload mmc 0 ${load_addr} ${processorName}${overlay_file}.dtbo; then
        echo "Applying user provided DT overlay ${overlay_file}.dtbo"
        fdt apply ${load_addr} || setenv overlay_error "true"
    fi
done


bootz $kernel_addr_r - $fdt_addr_r

So, what happens is the device tree overlays are merged in uboot with the dtb file loaded for the board using fdt command line tools.  This allows to change the board dtb without always recompiling it.

Post any questions you have.   So, spi and i2c are now using device tree overlays.

Here is the overlay for SPI:
/dts-v1/;
/plugin/;

/ {
    compatible = "allwinner,sun8i-h3";

    fragment@0 {
        target-path = "/aliases";
        __overlay__ {
            spi0 = "/soc/spi@01c68000";
            spi1 = "/soc/spi@01c69000";
        };
    };

    fragment@1 {
        target = <&spi0>;
        __overlay__ {

            #address-cells = <1>;
            #size-cells = <0>;
            status = "disabled";

            spidev@1 {
                compatible = "linux,spidev";
                reg = <0>;
                spi-max-frequency = <1000000>;
            };
        };
    };

    fragment@2 {
        target = <&spi1>;
        __overlay__ {

            #address-cells = <1>;
            #size-cells = <0>;
            status = "okay";

            spidev@2 {
                compatible = "linux,spidev";
                reg = <0>;
                spi-max-frequency = <25000000>;
            };
        };
    };
};


so, this completes the task of using overlays.  Next DHCP and zeroconfig.

Also, have a modification to EEM USB handler, to improve performance.  Also, thinking of adding a way to use several packets at once based on the size of the packet.