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linux_device_trees [2018/11/17 18:34]
rpjday
linux_device_trees [2018/12/11 13:03] (current)
rpjday [Internal wiki pages]
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 Stuff related to device trees and the Linux kernel, using examples from the current Linux kernel. Stuff related to device trees and the Linux kernel, using examples from the current Linux kernel.
  
-To do:+===== TO DO =====
  
   * overlays   * overlays
 +  * keywords (/plugin/, /​memreserve/,​ /​omit-if-no-ref/,​ /bits/)
 +
 +===== MISC (for now) =====
 +
 +  * "The unit-address must match the first address specified in the reg property of the node. If the node has no reg property, the @unit-address must be omitted and the node-name alone differentiates the node from other nodes at the same level in the tree. The binding for a particular bus may specify additional, more specific requirements for the format of reg and the unit-address."​
  
 ===== Some links ===== ===== Some links =====
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   * [[Device tree naming conventions]]   * [[Device tree naming conventions]]
   * [[Proper device tree design]]   * [[Proper device tree design]]
 +  * [[Device tree standard properties]]
 +  * [[Device tree node requirements]]
   * [[Comparing device trees with dtx_diff]]   * [[Comparing device trees with dtx_diff]]
 +  * [[Hierarchical device files]]
  
-===== Proper device tree design ===== 
- 
-==== One board, one .dts file ==== 
- 
-Every distinct board merits its own ''​.dts''​ file, as in: 
- 
-  * ''​am335x-boneblack.dts''​ 
-  * ''​am335x-boneblack-wireless.dts''​ 
-  * ''​am335x-boneblue.dts''​ 
-  * ''​am335x-bone.dts''​ 
-  * ''​am335x-bonegreen.dts''​ 
-  * ''​am335x-bonegreen-wireless.dts''​ 
- 
-==== Proper use of .dtsi files ==== 
- 
-There is **//no reason//** to make local copies of kernel-supplied ''​.dtsi''​ files and alter them; such files should be included as is, and //all// alterations should be made in the ''​.dts''​ file or a more general board-related ''​.dtsi''​ file supplied by that developer. Any alterations that involve actual //removal// of included content should be done via one of the two directives: 
- 
-  * ''/​delete-property/''​ 
-  * ''/​delete-node/''​ 
- 
-This functionality was introduced into the Linux kernel file ''​scripts/​dtc/​dtc-lexer.l''​ file in Sept of 2012: 
- 
-<​file>​ 
-commit cd296721a9645f9f28800a072490fa15458d1fb7 
-Author: Stephen Warren <​swarren@nvidia.com>​ 
-Date:   Fri Sep 28 21:25:59 2012 +0000 
- 
-    dtc: import latest upstream dtc 
-    ​ 
-    This updates scripts/dtc to commit 317a5d9 "dtc: zero out new label 
-    objects"​ from git://​git.jdl.com/​software/​dtc.git. 
-    ​ 
-    This adds features such as: 
-    * /bits/ syntax for cell data. 
-    * Math expressions within cell data. 
-    * The ability to delete properties or nodes. 
-    * Support for #line directives in the input file, which allows the use of 
-      cpp on *.dts. 
-    * -i command-line option (/include/ path) 
-    * -W/-E command-line options for error/​warning control. 
-    * Removal of spew to STDOUT containing the filename being compiled. 
-    * Many additions to the libfdt API. 
-    ​ 
-    Signed-off-by:​ Stephen Warren <​swarren@nvidia.com>​ 
-    Acked-by: Jon Loeliger <​jdl@jdl.com>​ 
-    Signed-off-by:​ Rob Herring <​rob.herring@calxeda.com>​ 
-</​file>​ 
- 
-Examples can be seen [[https://​elinux.org/​Device_Tree_Source_Undocumented|here]]. 
- 
-==== Examples of /​delete-node/​ ==== 
- 
-=== imx6dl-tx6s-8034.dts === 
- 
-<​file>​ 
-#include "​imx6dl.dtsi"​ 
-#include "​imx6qdl-tx6.dtsi"​ 
- 
-/ { 
-        model = "Ka-Ro electronics TX6S-8034 Module";​ 
-        compatible = "​karo,​imx6dl-tx6dl",​ "​fsl,​imx6dl";​ 
- 
-        aliases { 
-                display = &​display;​ 
-                ipu1 = &ipu1; 
-        }; 
- 
-        cpus { 
-                /​delete-node/​ cpu@1; 
-        }; 
-</​file>​ 
- 
-=== imx6q-utilite-pro.dts === 
- 
-<​file>​ 
-#include <​dt-bindings/​input/​input.h>​ 
-#include "​imx6q-cm-fx6.dts"​ 
- 
-/ { 
-        model = "​CompuLab Utilite Pro"; 
-        compatible = "​compulab,​utilite-pro",​ "​compulab,​cm-fx6",​ "​fsl,​imx6q";​ 
-        ​ 
- ... 
- 
-}; 
- 
-/* 
- * A single IPU is not able to drive both display interfaces available on the 
- * Utilite Pro at high resolution due to its bandwidth limitation. Since the 
- * tfp410 encoder is wired up to IPU1, sever the link between IPU1 and the 
- * SoC-internal Designware HDMI encoder forcing the latter to be connected to 
- * IPU2 instead of IPU1. 
- */ 
-/​delete-node/&​ipu1_di0_hdmi;​ 
-/​delete-node/&​hdmi_mux_0;​ 
-/​delete-node/&​ipu1_di1_hdmi;​ 
-/​delete-node/&​hdmi_mux_1;​ 
-</​file>​ 
- 
- 
-==== Examples of /​delete-property/​ ==== 
- 
-=== imx6qp.dtsi === 
- 
-<​file>​ 
-#include "​imx6q.dtsi"​ 
- 
-/ { 
-        soc { 
-        ​ 
-        ... 
-        ​ 
-}; 
- 
-&fec { 
-        /​delete-property/​interrupts-extended;​ 
-        interrupts = <0 118 IRQ_TYPE_LEVEL_HIGH>,​ 
-                     <0 119 IRQ_TYPE_LEVEL_HIGH>;​ 
-}; 
-</​file>​ 
- 
-=== imx6ul-tx6ul-mainboard.dts === 
- 
-<​file>​ 
-#include "​imx6ul.dtsi"​ 
-#include "​imx6ul-tx6ul.dtsi"​ 
- 
-/ { 
-        model = "Ka-Ro electronics TXUL-0010 Module on TXUL Mainboard";​ 
-        compatible = "​karo,​imx6ul-tx6ul",​ "​fsl,​imx6ul";​ 
- 
-        aliases { 
-                lcdif_24bit_pins_a = &​pinctrl_disp0_3;​ 
-                mmc0 = &​usdhc1;​ 
-                /​delete-property/​ mmc1; 
-                serial2 = &uart3; 
-                serial4 = &uart5; 
-        }; 
-        /​delete-node/​ sound; 
-}; 
- 
-... 
- 
-&usdhc1 { 
-        pinctrl-0 = <&​pinctrl_usdhc1>;​ 
-        non-removable;​ 
-        /​delete-property/​ cd-gpios; 
-        cap-sdio-irq;​ 
-}; 
- 
-&uart1 { 
-        pinctrl-0 = <&​pinctrl_uart1>;​ 
-        /​delete-property/​ uart-has-rtscts;​ 
-}; 
- 
-&uart2 { 
-        pinctrl-0 = <&​pinctrl_uart2>;​ 
-        /​delete-property/​ uart-has-rtscts;​ 
-        status = "​okay";​ 
-}; 
-</​file>​ 
linux_device_trees.1542479660.txt.gz ยท Last modified: 2018/11/17 18:34 by rpjday