Re: [PATCH] RISC-V: cmdline: Add support for 'memmap' parameter

[Charlie Jenkins <charlie@rivosinc.com>]

On Tue, Jun 18, 2024 at 08:08:42PM +0800, Yunhui Cui wrote:
> Implement support for parsing 'memmap' kernel command line parameter.
> 
> This patch covers parsing of the following two formats for 'memmap'
> parameter values:
> 
> - nn[KMG]@ss[KMG]
> - nn[KMG]$ss[KMG]
> 
> ([KMG] = K M or G (kilo, mega, giga))
> 
> These two allowed formats for parameter value are already documented
> in file kernel-parameters.txt in Documentation/admin-guide folder.
> Some architectures already support them, but Mips did not prior to

Copy-paste from a Mips patch? Should say riscv :)

It looks like this code is duplicated from xtensa and is effectively the
same as mips. Can this code be placed in a generic file so that the code
can be shared between mips, riscv, and xtensa -- maybe a new config that
gets selected by mips/riscv/xtensa?

- Charlie

> this patch.
> 
> Excerpt from Documentation/admin-guide/kernel-parameters.txt:
> 
> memmap=nn[KMG]@ss[KMG]
> [KNL] Force usage of a specific region of memory.
> Region of memory to be used is from ss to ss+nn.
> 
> memmap=nn[KMG]$ss[KMG]
> Mark specific memory as reserved.
> Region of memory to be reserved is from ss to ss+nn.
> Example: Exclude memory from 0x18690000-0x1869ffff
> memmap=64K$0x18690000
> or
> memmap=0x10000$0x18690000
> 
> There is no need to update this documentation file with respect to
> this patch.
> 
> Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
> ---
>  arch/riscv/mm/init.c | 50 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index e3405e4b99af..7be7ec3092ad 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -208,6 +208,56 @@ static int __init early_mem(char *p)
>  }
>  early_param("mem", early_mem);
>  
> +static void __init parse_memmap_one(char *p)
> +{
> +	char *oldp;
> +	unsigned long start_at, mem_size;
> +
> +	if (!p)
> +		return;
> +
> +	oldp = p;
> +	mem_size = memparse(p, &p);
> +	if (p == oldp)
> +		return;
> +
> +	switch (*p) {
> +	case '@':
> +		start_at = memparse(p + 1, &p);
> +		memblock_add(start_at, mem_size);
> +		break;
> +
> +	case '$':
> +		start_at = memparse(p + 1, &p);
> +		memblock_reserve(start_at, mem_size);
> +		break;
> +
> +	case 0:
> +		memblock_reserve(mem_size, -mem_size);
> +		break;
> +
> +	default:
> +		pr_warn("Unrecognized memmap syntax: %s\n", p);
> +		break;
> +	}
> +}
> +
> +static int __init parse_memmap_opt(char *str)
> +{
> +	while (str) {
> +		char *k = strchr(str, ',');
> +
> +		if (k)
> +			*k++ = 0;
> +
> +		parse_memmap_one(str);
> +		str = k;
> +	}
> +
> +	return 0;
> +}
> +early_param("memmap", parse_memmap_opt);
> +
>  static void __init setup_bootmem(void)
>  {
>  	phys_addr_t vmlinux_end = __pa_symbol(&_end);
> -- 
> 2.20.1
> 
> 
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