linux-kernel - Re: [PATCH] RISC-V: Relocate the kernel relative to a DRAM base.

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Message-ID: <CAMj1kXGm9d7SdBoozEoOP4G6ETmNiZR8kum91RVc_4eUTroE2w@mail.gmail.com>
Date:   Tue, 27 Apr 2021 14:42:59 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Nikita Ermakov <arei@...linux.org>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atish.patra@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RISC-V: Relocate the kernel relative to a DRAM base.

On Tue, 27 Apr 2021 at 14:07, Nikita Ermakov <arei@...linux.org> wrote:
>
> Try to get the base of the DRAM from a DTB to use it as a lowest address
> in physical memory to relocate the kernel. If it is not possible to
> obtain the base from a /memory node of the DTB let's make an assumption
> that the DRAM base at the beginning of the memory.
>

Why?

> Signed-off-by: Nikita Ermakov <arei@...linux.org>
> ---
>  drivers/firmware/efi/libstub/riscv-stub.c | 39 ++++++++++++++++++++++-
>  1 file changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/libstub/riscv-stub.c b/drivers/firmware/efi/libstub/riscv-stub.c
> index 380e4e251399..1b5944276e1a 100644
> --- a/drivers/firmware/efi/libstub/riscv-stub.c
> +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> @@ -46,6 +46,39 @@ static u32 get_boot_hartid_from_fdt(void)
>         return fdt32_to_cpu(*prop);
>  }
>
> +static unsigned long get_dram_base_from_fdt(void)
> +{
> +       const void *fdt;
> +       int node, len;
> +       const fdt32_t *addr_cells;
> +       const void *prop;
> +
> +       fdt = get_efi_config_table(DEVICE_TREE_GUID);
> +       if (!fdt)
> +               return ULONG_MAX;
> +
> +       node = fdt_path_offset(fdt, "/");
> +       if (node < 0)
> +               return ULONG_MAX;
> +
> +       addr_cells = fdt_getprop((void *)fdt, node, "#address-cells", &len);
> +       if (!addr_cells)
> +               return ULONG_MAX;
> +
> +       node = fdt_path_offset(fdt, "/memory");
> +       if (node < 0)
> +               return ULONG_MAX;
> +
> +       prop = fdt_getprop((void *)fdt, node, "reg", &len);
> +       if (!prop)
> +               return ULONG_MAX;
> +
> +       if (fdt32_to_cpu(*addr_cells) > 1)
> +               return fdt64_to_cpu(*((fdt64_t *)prop));
> +       else
> +               return fdt32_to_cpu(*((fdt32_t *)prop));
> +}
> +
>  efi_status_t check_platform_features(void)
>  {
>         hartid = get_boot_hartid_from_fdt();
> @@ -97,7 +130,11 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
>          * lowest possible memory region as long as the address and size meets
>          * the alignment constraints.
>          */
> -       preferred_addr = MIN_KIMG_ALIGN;
> +       preferred_addr = get_dram_base_from_fdt();
> +       if (preferred_addr == ULONG_MAX)
> +               preferred_addr = MIN_KIMG_ALIGN;
> +       else
> +               preferred_addr += MIN_KIMG_ALIGN;
>         status = efi_relocate_kernel(image_addr, kernel_size, *image_size,
>                                      preferred_addr, MIN_KIMG_ALIGN, 0x0);
>
> --
> 2.29.3
>