How to set up a Linux device tree for use with the bit-bang MDIO GPIO driver

To set up a Linux device tree for use with the bit-bang MDIO GPIO driver, you need to make the necessary modifications to the device tree source (DTS) file and compile it into a device tree blob (DTB) that the Linux kernel can understand. Here are the steps to do so:

1. Locate the DTS file for your specific hardware board. This file contains the device tree description for the board and can usually be found in the arch/arm/boot/dts directory of the Linux kernel source.

2. Open the DTS file in a text editor.

3. Search for the Ethernet controller node that you want to configure for bit-bang MDIO.

4. Add the following properties to the Ethernet controller node:

mdio-gpio {
      compatible = "gpio-bitbang-mdio";
      #gpio-cells = <2>;
      reset-gpios = <&gpioX Y GPIO_ACTIVE_HIGH>;
      mdio-gpios = <&gpioX Z GPIO_ACTIVE_HIGH>;
};

Replace gpioX with the actual GPIO controller and Y and Z with the specific GPIO pin numbers to be used for the reset and MDIO lines, respectively. The GPIO_ACTIVE_HIGH property indicates the active state of the GPIO lines.

5. Save the changes to the DTS file.

6. Compile the DTS file into a DTB using the Device Tree Compiler (dtc). Run the following command in the Linux kernel source directory:

dtc -I dts -O dtb -o devicetree.dtb path/to/dts/file.dts

Replace path/to/dts/file.dts with the actual path to your modified DTS file.

7. Place the resulting DTB file (devicetree.dtb) in the appropriate location on your target device. The exact location depends on your specific device and bootloader configuration. Typically, it should be placed in the /boot directory or the root directory of the boot partition.

8. Boot your Linux kernel with the modified device tree. This can be done by specifying the DTB file as a kernel command line parameter or by configuring your bootloader to load the modified DTB.

Once the Linux kernel boots with the modified device tree, it will recognize the bit-bang MDIO configuration for the Ethernet controller and use the specified GPIO lines for MDIO communication