Devicetree: Difference between revisions
Created page with "The '''devicetree''' (device tree, DT (DTS/DTB)) is a data structure which holds information about all components present on a device. This data is structured in nested nodes with key/value property pairs for configuration. In simpler terms - a devicetree tells the kernel (or another DT-compatible piece of software/firmware like a bootloader) where each component is in register space/on an I2C or similar bus, and what settings to use to set it up. It is the basic mechan..." |
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The <code>dtc</code> tool handles compiling DTS files into DTBs, as well as decompiling DTBs back into DTS. | The <code>dtc</code> tool handles compiling DTS files into DTBs, as well as decompiling DTBs back into DTS. | ||
=== Device Tree Source basics === | |||
Here is a very simple DTS file to explain the basics of what you might see in a device tree source file: | |||
<syntaxhighlight lang="dts"> | |||
/dts-v1/; | |||
/ { | |||
#address-cells = <1>; | |||
#size-cells = <1>; | |||
my_node: node1@1000 { | |||
compatible = "vendor,foo"; | |||
reg = <0x1000 0x54>; | |||
vendor,bar-factor = <0x2a>; | |||
}; | |||
node2@2000 { | |||
compatible = "vendor,bar"; | |||
reg = <0x2000 0xa4>; | |||
vendor,baz-companion = <&my_node>; | |||
}; | |||
i2c-controller@3000 { | |||
compatible = "vendor,foobar-i2c"; | |||
reg = <0x3000 0x800>; | |||
#address-cells = <1>; | |||
#size-cells = <0>; | |||
sensor@10 { | |||
compatible = "vendor,baz-sensor"; | |||
reg = <0x10>; | |||
}; | |||
}; | |||
}; | |||
</syntaxhighlight> | |||
In this example, we define an empty DTS; in its root node (<code>/</code>), we place three nodes: a node named "node1" with a label "my_node" at address 0x1000, a node named "node2" at address 0x2000, and a node named "i2c-controller" at address 0x3000. | |||
A node contains: | |||
* A <code>compatible</code> value (here <code>"vendor,foo"</code>). This specifies what kind of component it is; Linux uses this information to load the correct driver. | |||
* A <code>reg</code> value. In this case, the first parameter is the base address in memory (<code>0x1000</code>), and the second is the size it occupies (<code>0x54</code>). The amount of cells for the address and size are specified by the <code>#address-cells</code> and <code>#size-cells</code> properties of the root node, respectively. | |||
** You might notice that the i2c-controller node defines another set of these <code>#address-cells</code> and <code>#size-cells</code> properties - this is because I2C devices contain their own subdevices with addresses ranging from 0x08 to 0x7f (todo verify), and they do not use a size. | |||
* A custom vendor-specific property, <code>vendor,bar-factor</code>, which takes a number. | |||
On node 2 there is also a property, <code>vendor,baz-companion</code>, which takes a pointer to another node - here the one we labeled "my_node". | |||
== Verifying device tree bindings and device tree sources == | == Verifying device tree bindings and device tree sources == | ||
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** [https://docs.kernel.org/devicetree/bindings/writing-bindings.html DOs and DON’Ts for designing and writing Devicetree bindings] | ** [https://docs.kernel.org/devicetree/bindings/writing-bindings.html DOs and DON’Ts for designing and writing Devicetree bindings] | ||
** [https://docs.kernel.org/devicetree/bindings/submitting-patches.html Submitting Devicetree (DT) binding patches] | ** [https://docs.kernel.org/devicetree/bindings/submitting-patches.html Submitting Devicetree (DT) binding patches] | ||
* On elinux.org: | |||
** [https://elinux.org/Device_Tree_Reference Device Tree Reference] | |||
** [https://elinux.org/Device_Tree_Reference Device Tree Usage] | |||
== References == | == References == | ||