Documentation/devicetree/usage-model.rst

1 .. SPDX-License-Identifier: GPL-2.0
17 The "Open Firmware Device Tree", or simply Devicetree (DT), is a data
44 ----------
45 The DT was originally created by Open Firmware as part of the
46 communication method for passing data from Open Firmware to a client
52 Since Open Firmware is commonly used on PowerPC and SPARC platforms,
56 In 2005, when PowerPC Linux began a major cleanup and to merge 32-bit
57 and 64-bit support, the decision was made to require DT support on all
58 powerpc platforms, regardless of whether or not they used Open
59 Firmware.  To do this, a DT representation called the Flattened Device
61 blob without requiring a real Open Firmware implementation.  U-Boot,
66 existing non-DT aware firmware.
74 -------------
79 -------------------
88 per-machine hard coded selections.
101 ---------------------------
108 machine-specific fixups.
127 	compatible = "ti,omap3-beagleboard", "ti,omap3450", "ti,omap3";
128 	compatible = "ti,omap3-beagleboard-xm", "ti,omap3450", "ti,omap3";
130 Where "ti,omap3-beagleboard-xm" specifies the exact model, it also
175 matches on "ti,omap3-beagleboard".
184 -------------------------
186 firmware to the kernel, so also gets used to pass in runtime and
195 		initrd-start = <0xc8000000>;
196 		initrd-end = <0xc8200000>;
199 The bootargs property contains the kernel arguments, and the initrd-*
201 initrd-end is the first address after the initrd image, so this doesn't
204 platform-specific configuration data.
221 ---------------------
226 This is also when machine-specific setup hooks will get called, like
232 As can be guessed by the names, .init_early() is used for any machine-
245 registering it en-masse in .init_machine().  When DT is used, then
263 	#address-cells = <1>;
264 	#size-cells = <1>;
265 	interrupt-parent = <&intc>;
276 		compatible = "nvidia,tegra20-soc", "simple-bus";
277 		#address-cells = <1>;
278 		#size-cells = <1>;
281 		intc: interrupt-controller@50041000 {
282 			compatible = "nvidia,tegra20-gic";
283 			interrupt-controller;
284 			#interrupt-cells = <1>;
289 			compatible = "nvidia,tegra20-uart";
295 			compatible = "nvidia,tegra20-i2s";
302 			compatible = "nvidia,tegra20-i2c";
303 			#address-cells = <1>;
304 			#size-cells = <0>;
317 		compatible = "nvidia,harmony-sound";
318 		i2s-controller = <&i2s1>;
319 		i2s-codec = <&wm8903>;
378 and register platform_devices for /soc/interrupt-controller, /soc/serial,
395 "simple-bus" is defined in the Devicetree Specification as a property
397 could be written to just assume simple-bus compatible nodes will
404 ------------------------