Efi loader module have its own memory management that flags as reserved the area between ram_top to ram_end (currently where dt reserved-memory is falling). uboot lmb updates reserved-memory by adding these efi loader module areas (see lmb_reserve_common->efi_lmb_reserve).
On our system (AM62xx SoC, 512MB RAM) we have some reserved-memory specified in the device tree (used for comunication with other microcontroller on the SoC, OPTEE, ...) falling in the DDR range between 456 and 512 MB.
Normally U-Boot relocate itself at the end of DDR so it overlap this reserved-memory and this of course does not work [1].
In this case U-Boot prints the following errors:
ERROR: reserving fdt memory region failed (addr=9c800000 size=300000) ERROR: reserving fdt memory region failed (addr=9cb00000 size=100000) ... ERROR: reserving fdt memory region failed (addr=9e800000 size=1800000)
because U-Boot reserved area (lmb_flag LMB_NONE) overlaps with the FDT reserve memories (lmb_flag LMB_NOMAP).
To fix this I moved the U-Boot relocation address, implementing board_get_usable_ram_top() and therefore setting gd->ram_top to a lower value with no overlap (448 MB).
The memory map is: +---------------+ 512 MB |DT reserved-mem| +---------------+ 456 MB |free space | +---------------+ 448 MB (ram_top) | | |uboot | | | +---------------+ 0 MB
This is working fine (the board is able to boot, no memory overlaps) ...
however, in this configuration U-Boot we still have some errors prints while loading linux dtb:
ERROR: reserving fdt memory region failed (addr=9cb00000 size=100000 flags=4) ERROR: reserving fdt memory region failed (addr=9cc00000 size=e00000 flags=4) ERROR: reserving fdt memory region failed (addr=9da00000 size=100000 flags=4) ERROR: reserving fdt memory region failed (addr=9db00000 size=c00000 flags=4) ERROR: reserving fdt memory region failed (addr=9e780000 size=80000 flags=4) ERROR: reserving fdt memory region failed (addr=9e800000 size=1800000 flags=4)
And the reason of these error is complete different: The efi loader lmb memory reservation (lib/lmb.c:efi_lmb_reserve()) is wrongly reserving some area.
1) lib/lmb.c:lmb_reserve_common() reserve these memories: ~415M - 448M u-boot reserved area (lmb_flag LMB_NONE) 456M - 512M fdt reserved-memory (lmb_flag LMB_NOMAP)
2) lib/lmb.c:efi_lmb_reserve() reserve a region just before u-boot reserved area. This is not coalesced/merged with the u-boot reserved area because it is not contiguous.
This is the reserved-memory array at this point: ~414M - ~414M efi loader reserved area (lmb_flag LMB_NONE) ~415M - 448M u-boot reserved area (lmb_flag LMB_NONE) 456M - 512M fdt reserved-memory (lmb_flag LMB_NOMAP)
3) lib/lmb.c:efi_lmb_reserve() reserve some more areas. In the last two steps efi loader add some reserved area that overlap u-boot and fdt reserved area BUT they are also contiguous to the "efi loader reserved area". The very last step reserve also area between ram_top (448M) to ram_end (512M)
We fall in this condition (where we have overlapping areas!): ~414M - 512M efi loader reserved area (lmb_flag LMB_NONE) ~415M - 448M u-boot reserved area (lmb_flag LMB_NONE) 456M - 512M fdt reserved-memory (lmb_flag LMB_NOMAP)
4) Now, while loading the linux fdt the reserved-memory areas are checked toward efi loader reserved area, they overlap, BUT they have different lmb_flag. So we get the ERROR print.
Hopefully this is clear, I undestand is not that obvious ...
IMO we have two different bugs: - there is nothing that prevent that coalesced area may overlap other areas (while lmb module expect that there aren't overlapping areas) - efi loader (correctly) reserve between ram_top and ram_end BUT this area is reserved by fdt.
One potential solution could be to override efi_add_known_memory() and set ram_top = ram_end, e.g.
- efi_add_conventional_memory_map(ram_start, ram_end, ram_top); + efi_add_conventional_memory_map(ram_start, ram_end, ram_end);
but this does not really seems like something that should ve overridden at the board level.
Any suggestion?
Emanuele