Understand the role and usage of Linux DTS

In the development of embedded Linux systems, the Device Tree (Device Tree, referred to as DTS) is a way to describe hardware devices and their The data structure of connection relationships and attributes in the system. The device tree enables the Linux kernel to run flexibly on different hardware platforms without modifying the kernel. In this article, the function and usage of Linux DTS will be introduced, and specific code examples will be provided to help readers better understand.

1. The function of the device tree

The main function of the device tree is to describe the information of the hardware device, including but not limited to the hardware type, address, interrupt number, GPIO pin, etc., and stipulates The connection relationship between these hardware devices. Through the device tree, the Linux kernel can dynamically identify hardware devices and their attributes during the startup process, thereby correctly configuring hardware resources and enabling the kernel to communicate with hardware devices smoothly.

In addition, the device tree can also realize the reuse of hardware modules by describing device tree fragments (*.dtsi files), thereby improving the maintainability and reusability of the code. By combining different device tree fragments, hardware resources can be flexibly configured to facilitate customization of different hardware platforms.

2. Related concepts of device tree

When using device tree, you need to understand the following important concepts:

• Device tree source file ( DTS): The device tree source file is a text file used to describe hardware device information, usually with a .dts extension. When the Linux kernel is compiled, the device tree source file will be compiled into a binary device tree file (*.dtb) for use by the kernel.
• Device tree node: Each hardware device or node in the device tree has a corresponding device tree node. Each node contains information related to the hardware device, such as device type, address, interrupt number, register address, etc.
• Device tree binding: Device tree binding refers to the process of binding device tree nodes to corresponding device drivers. Nodes in the device tree load the corresponding driver by matching the device tree with the device driver.

3. The basic structure of the device tree

The basic structure of the device tree source file consists of nodes and properties. Nodes are used to describe hardware devices, and attributes are used to describe attribute information of nodes. The following is a simple device tree source file example:

/dts-v1/;

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

/ {
    compatible = "myboard, mydevice";
    
    mydevice {
        compatible = "mydevice";
        reg = <0x100000 0x1000>;
        interrupts = <0 2>;
        gpio = <&gpio1 10 GPIO_ACTIVE_LOW>;
    };
};

In the above example, mydevice represents a node of a hardware device, including the device's compatible attribute, register address, and interrupt number. and GPIO pin information.

4. Example of using the device tree

The following will take an LED driver as an example to show how to use the device tree to describe the hardware device and bind it to the device driver.

4.1 Write the device tree source file

First, create an LED device tree source file led.dts, and add the following content:

/dts-v1/;

/ {
    compatible = "myboard, myled";
    
    myled {
        compatible = "myled";
        reg = <0x200000 0x1000>;
        gpio = <&gpio1 20 GPIO_ACTIVE_LOW>;
    };
};

4.2 Write LED device driver

Next, write LED device driverled_driver.c, the sample code is as follows:

#include <linux/module.h>
#include <linux/platform_device.h>

static struct platform_device led_device = {
    .name = "myled",
    .id = -1,
};

static int __init led_driver_init(void)
{
    platform_device_register(&led_device);
    pr_info("LED driver initialized
");
    return 0;
}

static void __exit led_driver_exit(void)
{
    platform_device_unregister(&led_device);
    pr_info("LED driver exited
");
}

module_init(led_driver_init);
module_exit(led_driver_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Author Name");
MODULE_DESCRIPTION("LED Driver");

4.3 Modify the Makefile and compile the kernel

Add compilation rules in the driver's Makefile, and compile the kernel to generate the device tree binary file led.dtb:

obj-m += led_driver.o

all:
    make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -C /path/to/kernel M=$(PWD) modules
    dtc -I dts -O dtb -o led.dtb led.dts

4.4 Loading the device tree and driver

in Linux During the startup process, load the device tree file led.dtb:

# cp led.dtb /boot/
# echo "dtb=led.dtb" >> /boot/uEnv.txt

and then load the LED device driver:

# insmod led_driver.ko

Conclusion

Through the above code example , readers can have a deeper understanding of the role and usage of the device tree in the Linux kernel. The device tree provides a flexible and extensible hardware description method, allowing the Linux kernel to adapt to the needs of different hardware platforms. In actual development, rational use of device trees can greatly simplify the development process of embedded systems and improve development efficiency.

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