[PATCH v2] RISC-V: cmdline: Add support for 'memmap' parameter

[Palmer Dabbelt]

On Mon, 22 Jul 2024 14:13:14 PDT (-0700), punit.agrawal at bytedance.com wrote:
> Hi Palmer,
>
> Charlie Jenkins <charlie at rivosinc.com> writes:
>
>> On Mon, Jun 24, 2024 at 08:37:39PM +0800, Yunhui Cui wrote:
>>> Add parsing of 'memmap' to use or reserve a specific region of memory.
>>>
>>> Implement the following memmap variants:
>>> - memmap=nn[KMG]@ss[KMG]: force usage of a specific region of memory;
>>> - memmap=nn[KMG]$ss[KMG]: mark specified memory as reserved;
>>>
>>> Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
>>> ---
>>>  arch/riscv/mm/init.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 46 insertions(+)
>>>
>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>> index e3405e4b99af..8e1d93ae5cb2 100644
>>> --- a/arch/riscv/mm/init.c
>>> +++ b/arch/riscv/mm/init.c
>>> @@ -208,6 +208,52 @@ static int __init early_mem(char *p)
>>>  }
>>>  early_param("mem", early_mem);
>>>
>>> +static void __init parse_memmap_one(char *p)
>>> +{
>>> +	char *oldp;
>>> +	unsigned long start_at, mem_size;
>>> +
>>> +	if (!p)
>>> +		return;
>>> +
>>> +	oldp = p;
>>> +	mem_size = memparse(p, &p);
>>> +	if (p == oldp)
>>> +		return;
>>> +
>>> +	switch (*p) {
>>> +	case '@':
>>> +		start_at = memparse(p + 1, &p);
>>> +		memblock_add(start_at, mem_size);
>>> +		break;
>>> +
>>> +	case '$':
>>> +		start_at = memparse(p + 1, &p);
>>> +		memblock_reserve(start_at, mem_size);
>>> +		break;
>>> +
>>> +	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
>>>
>>
>> Reviewed-by: Charlie Jenkins <charlie at rivosinc.com>
>
> Another patch that looks good to get merged if there are no further
> comments.
>
> Any chance this can be picked up for this cycle?

Sorry for being slow here, but I don't understand the use case for this: 
we already get the memory map from the firmware, it seems like 
overriding that is just asking for issues.