How to enable SPI on BeagleV®-Fire

If You want to use the SPI periphery of the beagleV Fire from a user-space application, just like on a microcontroller, You need to modify the device tree: You must add the spidev node to the spi periphery so linux adds the /dev/spidev character device driver on boot. The device tree is located in an image file in /boot/firmware/beaglev_fire.itb This file is a “Flattened Image Tree (FIT) Format”. While booting, U-Boot is loading this file. This image contains the kernel image and the device tree blob. To add spidev node You must:

Extract the kernel image from the FIT image
Extract the device tree blob from the FIT image
Decompile the device tree blob to get the device tree source
Add the spidev node to the device tree source
Compile the device tree source
Add the kernel image and device tree blob to a new FIT image
Replace the FIT image

All can be done on the beagleV Fire board using the UART terminal.

Make a backup of the original FIT image:

beagle@BeagleV:~$ cp /boot/firmware/beaglev_fire.itb /boot/firmware/beaglev_fire.itb_bkp
beagle@BeagleV:~$ cp /boot/firmware/beaglev_fire.itb ~/
beagle@BeagleV:~$ cd

Let’s see what's inside the FIT image:

beagle@BeagleV:~$ dumpimage -l beaglev_fire.itb

Extract the kernel image from the FIT image:

beagle@BeagleV:~$ dumpimage -T flat_dt -p 0 beaglev_fire.itb -o Image

Extract the device tree blob from the FIT image:

beagle@BeagleV:~$ dumpimage -T flat_dt -p 1 beaglev_fire.itb -o beaglev_fire.dtb

Decompile the device tree blob to get the device tree source:

beagle@BeagleV:~$ dtc -I dtb -O dts -o beaglev_fire.dts beaglev_fire.dtb

Add the spidev node to the device tree source:

beagle@BeagleV:~$ nano beaglev_fire.dts

Press Alt-C to enable line numbers add these line after line 389:

				spidev@0{
					compatible = "rohm,dh2228fv";
					reg = <0>;
					spi-max-frequency = <4000000>;
				};

Ctrl+O to save Ctrl+X to exit

Compile the device tree source:

beagle@BeagleV:~$ dtc -I dts -O dtb -o beaglev_fire.dtb beaglev_fire.dts

Add the kernel image and device tree blob to a new FIT image:

beagle@BeagleV:~$ nano beaglev_fire.its

Paste this:

/dts-v1/;

/ {
    description = "U-Boot fitImage for the BeagleV-Fire";
    #address-cells = <1>;

    images {
        kernel {
            description = "Linux kernel";
            data = /incbin/("./Image");
            type = "kernel";
            arch = "riscv";
            os = "linux";
            compression = "gzip";
            load = <0x80200000>;
            entry = <0x80200000>;
            hash {
                algo = "sha256";
            };
        };
        base_fdt {
            description = "Flattened Device Tree Blob";
            data = /incbin/("./beaglev_fire.dtb");
            type = "flat_dt";
            arch = "riscv";
            compression = "none";
			load = <0x8a000000>;
            hash {
                algo = "sha256";
            };
        };
    };
    configurations {
        default = "kernel_dtb";
        kernel_dtb {
            description = "1 Linux kernel, FDT blob";
            kernel = "kernel";
            fdt = "base_fdt";
        };
        base_dtb {
            description = "Base FDT blob for BeagleV-Fire board";
            kernel = "unavailable";
            fdt = "base_fdt";
        };
    };
};