| Rob Herring | 4418482 | 2020-10-08 09:24:20 -0500 | [diff] [blame] | 1 | .. SPDX-License-Identifier: GPL-2.0 |
| 2 | |
| 3 | DeviceTree Booting |
| 4 | ------------------ |
| 5 | |
| 6 | There is one single 32bit entry point to the kernel at code32_start, |
| 7 | the decompressor (the real mode entry point goes to the same 32bit |
| 8 | entry point once it switched into protected mode). That entry point |
| 9 | supports one calling convention which is documented in |
| 10 | Documentation/x86/boot.rst |
| 11 | The physical pointer to the device-tree block is passed via setup_data |
| 12 | which requires at least boot protocol 2.09. |
| 13 | The type filed is defined as |
| 14 | |
| 15 | #define SETUP_DTB 2 |
| 16 | |
| 17 | This device-tree is used as an extension to the "boot page". As such it |
| 18 | does not parse / consider data which is already covered by the boot |
| 19 | page. This includes memory size, reserved ranges, command line arguments |
| 20 | or initrd address. It simply holds information which can not be retrieved |
| 21 | otherwise like interrupt routing or a list of devices behind an I2C bus. |