1. Basic Data Format

The device tree is a simple tree structure of nodes and properties. Properties are key-value pairs, and node may contain both properties and child nodes.

The following does show the format and structure of nodes and properties , but doesn't describe anything.

/dts-v1/;
/* '/' means single root node  */
/ {
    node1 {
        a-string-property = "A string";
        a-string-list-property = "first string", "second string";
        // hex is implied in byte arrays. no '0x' prefix is required
        a-byte-data-property = [01 23 34 56];
        child-node1 {
            first-child-property;
            second-child-property = <1>;
            a-string-property = "Hello, world";
        };
        child-node2 {
        };
    };
    node2 {
        an-empty-property;
        a-cell-property = <1 2 3 4>; /* each number (cell) is a uint32 */
        child-node1 {
        };
    };
};

(Note: *.dtsi header such like *.h to include dts source file.)

1.1 Device Node

Every device in the system is represented by a device tree node. node name form such like ,

<name>[@<unit-address>]

is a simple ascii string and can be up to 31 characters in length.

is included if the node describes a device with an address. In general, the unit address is the primary address used to access the device, and is listed in the node's reg property. We'll cover the reg property later in this document.

1.2 Node Property

1.2.1 'compatible' property

Every device node has a compatible property. compatible is a list of strings. The first string in the list specifies the exact device that the node represents in the form "<manufacturer>,<model>". The following strings represent other devices that the device is compatible with.

example for led setting ex3320-to-tm.dts

zyleds {
		compatible = "gpio-leds";
		led_green_inet {
			label = "zyled-green-inet";
			gpios = <&pio 4 GPIO_ACTIVE_LOW>;
			default-state = "off";
		};
};

corresponding driver linux-5.4.194/drivers/leds/leds-gpio.c by .compatible property.

static const struct of_device_id of_gpio_leds_match[] = {
	{ .compatible = "gpio-leds", },
	{},
};
static struct platform_driver gpio_led_driver = {
	.probe		= gpio_led_probe,
	.shutdown	= gpio_led_shutdown,
	.driver		= {
		.name	= "leds-gpio",
		.of_match_table = of_gpio_leds_match,
	},
};
module_platform_driver(gpio_led_driver);

1.2.2 'phandle' property

phandle 属性通过一个唯一的 u32 整数指向 DeviceTree 中的其他节点.

1.3 Addressing

Devices that are addressable use the following properties to encode address information into the device tree:

reg
#address-cells
#size-cells

1.4 Interrupts

2. Describe Virtual Sample Machine

This device contains following:

One 32bit ARM CPU
processor local bus attached to memory mapped serial port, spi bus controller, i2c controller, interrupt controller, and external bus bridge
256MB of SDRAM based at 0
2 Serial ports based at 0x101F1000 and 0x101F2000
GPIO controller based at 0x101F3000
SPI controller based at 0x10170000 with following devices
- MMC slot with SS pin attached to GPIO #1
External bus bridge with following devices
- SMC SMC91111 Ethernet device attached to external bus based at 0x10100000
- i2c controller based at 0x10160000 with following devices
  - Maxim DS1338 real time clock. Responds to slave address 1101000 (0x58)
- 64MB of NOR flash based at 0x30000000

/dts-v1/;

/ {
    compatible = "acme,coyotes-revenge";

    cpus {
        cpu@0 {
            compatible = "arm,cortex-a9";
        };
        cpu@1 {
            compatible = "arm,cortex-a9";
        };
    };

    serial@101F0000 {
        compatible = "arm,pl011";
    };

    serial@101F2000 {
        compatible = "arm,pl011";
    };

    gpio@101F3000 {
        compatible = "arm,pl061";
    };

    interrupt-controller@10140000 {
        compatible = "arm,pl190";
    };

    spi@10115000 {
        compatible = "arm,pl022";
    };

    external-bus {
        ethernet@0,0 {
            compatible = "smc,smc91c111";
        };

        i2c@1,0 {
            compatible = "acme,a1234-i2c-bus";
            rtc@58 {
                compatible = "maxim,ds1338";
            };
        };

        flash@2,0 {
            compatible = "samsung,k8f1315ebm", "cfi-flash";
        };
    };
};

4.4 KiB Raw Permalink Blame History