Re: [PATCH] RISC-V: Place DTB at 3GB boundary instead of 4GB

[Palmer Dabbelt <palmer@dabbelt.com>]

On Thu, 17 Dec 2020 13:48:26 PST (-0800), Atish Patra wrote:
> Currently, we place the DTB at 2MB from 4GB or end of DRAM which ever is
> lesser. However, Linux kernel can address only 1GB of memory for RV32.
> Thus, it can not map anything beyond 3GB (assuming 2GB is the starting address).
> As a result, it can not process DT and panic if opensbi dynamic firmware
> is used.
>
> Fix this by placing the DTB at 2MB from 3GB or end of DRAM whichever is lower.
>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
>  hw/riscv/boot.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
> index d62f3dc7581e..9e77b22e4d56 100644
> --- a/hw/riscv/boot.c
> +++ b/hw/riscv/boot.c
> @@ -203,9 +203,9 @@ uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
>       * We should put fdt as far as possible to avoid kernel/initrd overwriting
>       * its content. But it should be addressable by 32 bit system as well.
>       * Thus, put it at an aligned address that less than fdt size from end of
> -     * dram or 4GB whichever is lesser.
> +     * dram or 3GB whichever is lesser.
>       */
> -    temp = MIN(dram_end, 4096 * MiB);
> +    temp = MIN(dram_end, 3072 * MiB);
>      fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
>
>      fdt_pack(fdt);

Presumably this was the cause of that 32-bit boot issue?