Creating A devicetree.cb

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Documentation is now handled by the same processes we use for code: Add something to the Documentation/ directory in the coreboot repo, and it will be rendered to https://doc.coreboot.org/. Contributions welcome!

This article should help people who are writting a devicetree.cb for their system.

What you will need

While running GNU/Linux on the vendor BIOS, collect the output from:

• dmesg
• lspci -ntvvv
• cat /proc/ioports

If you have support for your board in serialice you may wish to gather its output also.

Reading lspci output

The Peripheral Component Interconnect (PCI) is a standerdized local bus for attaching different hardwares to motherboard.

The lspci command reads the bus information and topology, its output format is given by example:

03:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS5209 PCI Express Card Reader (rev 01)
+------ +----------------------  +--------------------------------------------------------------
^       ^                        ^
|       |                        |
|       |                        Field 3: Name of device attached and its manufactured company name. 
|       Field 2: PCI slot name.
Field 1: PCI bus slot number.

Introduction

The mainboard's devicetree.cb file contains many build and platform configuration settings. One of the most important items is the mainboard device list.

A device needs to be listed in the mainboard devicetree.cb if it requires more setup than standard PCI initialization (resource allocation). Typically, that includes the CPU, northbridge, southbridge, and Super I/O. These devices are usually required for system specific configuration as well as indicate the system bus structure (pci_domain).

When a device in devicetree.cb is found during the coreboot PCI/system scan process the functions to do customized initialization are called via the device_operations and the chip_operations structures. You will find these structures in the devices source files.

Keywords & Symbols

chip, device, register,on,off,pci,ioapic,pnp,i2c,lapic,cpu_cluster,domain,irq,drq,io,ioapic_irq,inherit,subsystemid,end,=

Syntax

• ioapic_irq

ioapic_irq: ioapic_irq number-literal pciint number-literal

rewrite this in BNF notation..

Grammar

Literals

Literal values types are defined and thus consumed by the following regular expressions:

• Hex

0x[0-9a-fA-F.]+
 
[0-9a-fA-F.]+

• Decimals

[0-9.]+

• PCI Interrupts

INT[A-D]

• Strings

\"[^\"]+\"
 
[^ \n\t]+

NOTES

See source util/sconfig/sconfig.* for devicetree compiler..

Examples

NorthBridge

..