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LoongArch: Support mem=<size> kernel parameter

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The LoongArch mem= parameter parser was previously limited to the
mem=<size>@<start> format. This was inconvenient for the common use
case of simply capping the total system memory, as it forced users to
manually specify a start address. It was also inconsistent with the
behavior on other architectures.

This patch enhances the parser in early_parse_mem() to also support the
more user-friendly mem=<size> format. The implementation now checks for
the presence of the '@' symbol to determine the user's intent:

- If mem=<size> is provided (no '@'), the kernel now calls
  memblock_enforce_memory_limit(). This trims memory from the top down
  to the specified size.
- If mem=<size>@<start> is provided, the original behavior is retained
  for backward compatibility. This allows for defining specific memory
  banks.

This change introduces an important usage rule reflected in the code's
comments: the mem=<size> format should only be specified once on the
kernel command line. It acts as a single, global cap on total memory. In
contrast, the mem=<size>@<start> format can be specified multiple times
to define several distinct memory regions.

Signed-off-by: Ming Wang <wangming01@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Ming Wang 2025-08-03 22:49:47 +08:00 committed by Huacai Chen
parent a1a81b5477
commit 243f8de49f
1 changed files with 10 additions and 8 deletions
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18
arch/loongarch/kernel/setup.c
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@ -191,6 +191,16 @@ static int __init early_parse_mem(char *p)
return -EINVAL;
}
start = 0;
size = memparse(p, &p);
if (*p == '@') /* Every mem=... should contain '@' */
start = memparse(p + 1, &p);
else { /* Only one mem=... is allowed if no '@' */
usermem = 1;
memblock_enforce_memory_limit(size);
return 0;
}
/*
* If a user specifies memory size, we
* blow away any automatically generated
@ -201,14 +211,6 @@ static int __init early_parse_mem(char *p)
memblock_remove(memblock_start_of_DRAM(),
memblock_end_of_DRAM() - memblock_start_of_DRAM());
}
start = 0;
size = memparse(p, &p);
if (*p == '@')
start = memparse(p + 1, &p);
else {
pr_err("Invalid format!\n");
return -EINVAL;
}
if (!IS_ENABLED(CONFIG_NUMA))
memblock_add(start, size);