Documentation/devicetree/usage-model.rst

1 .. SPDX-License-Identifier: GPL-2.0
21 machine.
44 ----------
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
61 blob without requiring a real Open Firmware implementation.  U-Boot,
66 existing non-DT aware firmware.
71 out of mainline (nios) have some level of DT support.
74 -------------
78 2.1 High Level View
79 -------------------
88 per-machine hard coded selections.
101 ---------------------------
103 specific machine.  In a perfect world, the specific platform shouldn't
107 machine during early boot so that it has the opportunity to run
108 machine-specific fixups.
110 In the majority of cases, the machine identity is irrelevant, and the
111 kernel will instead select setup code based on the machine's core
122 with the exact name of the machine, followed by an optional list of
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
137 cautioned about doing so at the board level since there is typically a
138 high level of change from one board to another, even within the same
140 board claims to be compatible with another.  For the top level, it is
153 machine.  After searching the entire table of machine_descs,
175 matches on "ti,omap3-beagleboard".
184 -------------------------
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
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