linux_device_trees
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linux_device_trees [2018/11/17 18:34] rpjday |
linux_device_trees [2018/12/11 13:03] 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 ===== | ||
| Line 46: | Line 51: | ||
| * [[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.txt ยท Last modified: 2018/12/11 13:03 by rpjday
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