Commit 243f8de4 authored Aug 03, 2025 by Ming Wang Committed by Huacai Chen Aug 03, 2025

LoongArch: Support mem=<size> kernel parameter



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>

parent a1a81b54

arch/loongarch/kernel/setup.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -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);