1.. SPDX-License-Identifier: GPL-2.0+
2.. sectionauthor:: Bin Meng <bmeng.cn@gmail.com>
3
4Coreboot
5========
6
7Build Instructions for U-Boot as coreboot payload
8-------------------------------------------------
9Building U-Boot as a coreboot payload is just like building U-Boot for targets
10on other architectures, like below::
11
12   $ make coreboot_defconfig
13   $ make all
14
15Test with coreboot
16------------------
17For testing U-Boot as the coreboot payload, there are things that need be paid
18attention to. coreboot supports loading an ELF executable and a 32-bit plain
19binary, as well as other supported payloads. With the default configuration,
20U-Boot is set up to use a separate Device Tree Blob (dtb). As of today, the
21generated u-boot-dtb.bin needs to be packaged by the cbfstool utility (a tool
22provided by coreboot) manually as coreboot's 'make menuconfig' does not provide
23this capability yet. The command is as follows::
24
25   # in the coreboot root directory
26   $ ./build/util/cbfstool/cbfstool build/coreboot.rom add-flat-binary \
27     -f u-boot-dtb.bin -n fallback/payload -c lzma -l 0x1110000 -e 0x1110000
28
29Make sure 0x1110000 matches CONFIG_SYS_TEXT_BASE, which is the symbol address
30of _x86boot_start (in arch/x86/cpu/start.S).
31
32If you want to use ELF as the coreboot payload, change U-Boot configuration to
33use CONFIG_OF_EMBED instead of CONFIG_OF_SEPARATE.
34
35To enable video you must enable these options in coreboot:
36
37   - Set framebuffer graphics resolution (1280x1024 32k-color (1:5:5))
38   - Keep VESA framebuffer
39
40At present it seems that for Minnowboard Max, coreboot does not pass through
41the video information correctly (it always says the resolution is 0x0). This
42works correctly for link though.
43
4464-bit U-Boot
45-------------
46
47In addition to the 32-bit 'coreboot' build there is a 'coreboot64' build. This
48produces an image which can be booted from coreboot (32-bit). Internally it
49works by using a 32-bit SPL binary to switch to 64-bit for running U-Boot. It
50can be useful for running UEFI applications, for example.
51
52This has only been lightly tested.
53
54
55Memory map
56----------
57
58  ==========  ==================================================================
59     Address  Region at that address
60  ==========  ==================================================================
61    ffffffff  Top of ROM (and last byte of 32-bit address space)
62    7a9fd000  Typical top of memory available to U-Boot
63              (use cbsysinfo to see where memory range 'table' starts)
64    10000000  Memory reserved by coreboot for mapping PCI devices
65              (typical size 2151000, includes framebuffer)
66     1920000  CONFIG_SYS_CAR_ADDR, fake Cache-as-RAM memory, used during startup
67     1110000  CONFIG_SYS_TEXT_BASE (start address of U-Boot code, before reloc)
68      110000  CONFIG_BLOBLIST_ADDR (before being relocated)
69      100000  CONFIG_PRE_CON_BUF_ADDR
70       f0000  ACPI tables set up by U-Boot
71              (typically redirects to 7ab10030 or similar)
72         500  Location of coreboot sysinfo table, used during startup
73  ==========  ==================================================================
74