Re: [RFC PATCH 2/3] riscv: Add early_param to decrease firmware region

[Anup Patel]

+Alex

On Tue, Nov 23, 2021 at 7:27 AM <guoren@xxxxxxxxxx> wrote:
>
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> Using riscv.fw_size in cmdline to tell the kernel what the
> firmware (opensbi) size is. Then reserve the proper size of
> firmware to save memory instead of the whole 2MB. It's helpful
> to satisfy a small memory system (D1s/F133 from Allwinner).
>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> Cc: Anup Patel <anup.patel@xxxxxxx>
> Cc: Atish Patra <atishp@xxxxxxxxxxxx>
> ---
>  arch/riscv/mm/init.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 920e78f8c3e4..f7db6d40213d 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -159,6 +159,15 @@ static int __init early_mem(char *p)
>  }
>  early_param("mem", early_mem);
>
> +static phys_addr_t firmware_size __initdata;
> +static int __init early_get_firmware_size(char *arg)
> +{
> +       firmware_size = memparse(arg, &arg);
> +
> +       return 0;
> +}
> +early_param("riscv.fwsz", early_get_firmware_size);
> +

We have avoided any RISC-V specific kernel parameter till now
and I don't think adding "riscv.fwsz" is the right approach.

OpenSBI adds a reserved memory node (mmode_resv@8000000)
to mark the memory where it is running as reserved. In fact, all
M-mode runtime firmware should be adding a reserved memory
node just like OpenSBI.

Regards,
Anup

>  static void __init setup_bootmem(void)
>  {
>         phys_addr_t vmlinux_end = __pa_symbol(&_end);
> @@ -224,7 +233,10 @@ static void __init setup_bootmem(void)
>         /*
>          * Reserve OpenSBI region and depends on PMP to deny accesses.
>          */
> -       memblock_reserve(__pa(PAGE_OFFSET), LOAD_OFFSET);
> +       if (firmware_size > PAGE_SIZE)
> +               memblock_reserve(__pa(PAGE_OFFSET), firmware_size);
> +       else
> +               memblock_reserve(__pa(PAGE_OFFSET), LOAD_OFFSET);
>
>         early_init_fdt_scan_reserved_mem();
>         dma_contiguous_reserve(dma32_phys_limit);
> --
> 2.25.1
>