Hi Zhuxu,
Thank you for your patches.
I am playing with Duo and Duo-256M and faced an interesting thing
regarding reserved-memory on these boards.
It looks like your patchset may cause a memory corruption
of U-Boot or coprocessor FW for Milk-V Duo.
DTS in U-Boot limits RAM to 63.25 MB:
memory@80000000 {
device_type = "memory";
reg = <0x80000000 0x3f40000>;
};
Because the last 0.75 MB (0xc0000) is reserved for coprocessor.
Kernel uses different approach by declaring all RAM and
relying on `reserved-memory` for coprocessor.
However, this doesn't work for U-Boot because it places its stack
and heap near the top of RAM, therefore region in the top of RAM
is not reserved. So coprocessor FW or U-Boot may be corrupted.
With your patches it also gives an ERROR during reserving (because the region
is already used by U-Boot itself):
U-Boot 2026.10-rc3-00007-g8e48ce755361 (Aug 27 2026 - 18:53:59 +0200)milkv_duo
DRAM: 64 MiB
ERROR: reserving fdt memory region failed (addr=83f40000 size=c0000 flags=2):
-17
Core: 23 devices, 15 uclasses, devicetree: separate
MMC: mmc@4310000: 0
Loading Environment from nowhere... OK
In: serial@4140000
Out: serial@4140000
Err: serial@4140000
Net:
Warning: ethernet@4070000 (eth0) using random MAC address - 0a:06:39:79:c7:ed
eth0: ethernet@4070000
milkv_duo# bdinfo
boot_params = 0x0000000000000000
DRAM bank = 0x0000000000000000
-> start = 0x0000000080000000
-> size = 0x0000000004000000
...
relocaddr = 0x0000000083f73000
reloc off = 0x0000000003d73000
...
fdt_blob = 0x000000008372ec60
lmb_dump_all:
memory.count = 0x1
memory[0] [0x80000000-0x83ffffff], 0x4000000 bytes, flags: none
reserved.count = 0x3
reserved[0] [0x80000000-0x8005ffff], 0x60000 bytes, flags: no-map
reserved[1] [0x8272b000-0x8272dfff], 0x3000 bytes, flags: no-notify,
no-overwrite
reserved[2] [0x8272ec50-0x83ffffff], 0x18d13b0 bytes, flags: no-overwrite
devicetree = separate
...
stack ptr = 0x000000008372e980
ram_top ptr = 0x0000000084000000
malloc base = 0x0000000083733000
boot hart = 0x0000000000000000
firmware fdt= 0x0000000080080000
milkv_duo# meminfo
DRAM: 64 MiB
Region Base Size End Gap
--------------------------------------------------------------------
code 83f73000 8cc30 83fffc30
malloc 83733000 840000 83f73000 0
board_info 83732fb0 50 83733000 0
global_data 83732e40 168 83732fa8 8
devicetree 8372ec60 41da 83732e3a 6
stack 8272ec50 1000000 8372ec50 10
lmb 8272ec50 0 8272ec50 0
lmb 8272b000 3c50 8272ec50 0
lmb 80000000 272b000 8272b000 0
free 80000000 0 80000000 0
Main branch with the original U-Boot DTS:
U-Boot 2026.10-rc3-00001-g7cbe3e32b6b4 (Aug 27 2026 - 18:30:42 +0200)milkv_duo
DRAM: 63.3 MiB
Core: 22 devices, 15 uclasses, devicetree: separate
MMC: mmc@4310000: 0
Loading Environment from nowhere... OK
In: serial@4140000
Out: serial@4140000
Err: serial@4140000
Net:
Warning: ethernet@4070000 (eth0) using random MAC address - 82:8a:04:d3:35:d0
eth0: ethernet@4070000
milkv_duo# bdinfo
boot_params = 0x0000000000000000
DRAM bank = 0x0000000000000000
-> start = 0x0000000080000000
-> size = 0x0000000003f40000
...
relocaddr = 0x0000000083eb3000
reloc off = 0x0000000003cb3000
...
fdt_blob = 0x00000000836705e0
lmb_dump_all:
memory.count = 0x1
memory[0] [0x80000000-0x83f3ffff], 0x3f40000 bytes, flags: none
reserved.count = 0x3
reserved[0] [0x80000000-0x8005ffff], 0x60000 bytes, flags: no-map
reserved[1] [0x8266d000-0x8266ffff], 0x3000 bytes, flags: no-notify,
no-overwrite
reserved[2] [0x826705d0-0x83f3ffff], 0x18cfa30 bytes, flags: no-overwrite
devicetree = separate
...
stack ptr = 0x0000000083670300
ram_top ptr = 0x0000000083f40000
malloc base = 0x0000000083673000
boot hart = 0x0000000000000000
firmware fdt= 0x0000000080080000
I'm not sure of a better solution here other than limiting the RAM node
to exclude the coprocessor region.
Best regards,
Andrei Lalaev
