dtb

Device Tree

• dtb - Device Tree Blob - device tree binary
  • hardware layout description
  • platform identification
  • runtime configuration
  • device population
• arch/<arch>/boot/dts/<board>
• CONFIG_ARM_APPENDED_DTB - dtb 在 kernel 之后
  • cat zImage board.dtb > my-zImage; mkimage ... -d my-zImage my-uImage
• CONFIG_ARM_ATAG_DTB_COMPAT
  • read ATAGS, update DT
• Embedded Power Architecture Platform Requirements (ePAPR)
• Device Tree Source - DTS
  • .dts - board-level definitions
    • 最终的 - include 多个 dtsi
  • .dtsi - included files, generally containing SoC-level definitions
  • e.g arch/arm64/boot/dtsGitHub Filetorvalds/linux/arch/arm64/boot/dts
• Device Tree Compiler
  • scripts/dtcGitHub Filetorvalds/linux/scripts/dtc
• Documentation/devicetree/bindings

Device Tree

• cpus
• memory
• chosen
  • defines parameters chosen or defined by the system firmware at boot time
• aliases
• buses

/ {
model = "Freescale i.MX28 Evaluation Kit";
compatible = "fsl,imx28-evk", "fsl,imx28";
memory {
  reg = <0x40000000 0x08000000>;
};
apb@80000000 {
  apbh@80000000 {  };
  apbx@80040000 {  };
};
ahb@80080000 {  };
sound {  };
leds {  };
backlight {  };
};

• of_machine_is_compatible

References

• Device treeWikipediaDevice tree
• lonzoc.gitbooks.io/device-tree-guide/content/devicetree_basic.html
• elinux.org/Device_Tree_Reference
• elinux.org/Device_Tree_Usage
• docs.kernel.org/devicetree/usage-model.html
• www.devicetree.org
• events.static.linuxfound.org/sites/events/files/slides/petazzoni-device-tree-dummies.pdf
  • bootloader
    1. before device tree - r1=machine_type, r2=ptr to ATAGS
    2. boot with device tree - r2=ptr to DTB