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x86: coreboot: Document the memory map

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Add information about memory usage when U-Boot is started from coreboot.
This is useful when debugging. Also, since coreboot takes a chunk of
memory in the middle of SDRAM for use by PCI devices, it can help avoid
overwriting this with a loaded kernel by accident.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
This commit is contained in:
Simon Glass 2021-06-27 17:51:08 -06:00 • committed by Bin Meng
parent 4dfe4b44cc
commit e74d0ec80b
1 changed files with 21 additions and 0 deletions
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doc/board/coreboot/coreboot.rst
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@ -50,3 +50,24 @@ works by using a 32-bit SPL binary to switch to 64-bit for running U-Boot. It
can be useful for running UEFI applications, for example.
This has only been lightly tested.
Memory map
----------
========== ==================================================================
Address Region at that address
========== ==================================================================
ffffffff Top of ROM (and last byte of 32-bit address space)
7a9fd000 Typical top of memory available to U-Boot
(use cbsysinfo to see where memory range 'table' starts)
10000000 Memory reserved by coreboot for mapping PCI devices
(typical size 2151000, includes framebuffer)
1920000 CONFIG_SYS_CAR_ADDR, fake Cache-as-RAM memory, used during startup
1110000 CONFIG_SYS_TEXT_BASE (start address of U-Boot code, before reloc)
110000 CONFIG_BLOBLIST_ADDR (before being relocated)
100000 CONFIG_PRE_CON_BUF_ADDR
f0000 ACPI tables set up by U-Boot
(typically redirects to 7ab10030 or similar)
500 Location of coreboot sysinfo table, used during startup
========== ==================================================================