[RFC PATCH 1/1] riscv: Add boot hartid to Device tree

[Ard Biesheuvel]

On Mon, 24 Feb 2020 at 23:20, Atish Patra <atish.patra at wdc.com> wrote:
>
> Linux booting protocol mandates that register "a0" contains the hartid.
> However, U-boot can not pass the hartid via a0 during EFI boot without
> breaking the UEFI specification.
>

It is not about breaking or violating the UEFI specification. It is
about the firmware using a conduit that is already being used to
describe the hardware to the OS to pass an extra piece of information
that the OS needs.

> Add a DT node under chosen node to indicate the boot hartid. EFI stub
> in Linux kernel will parse this node and pass it to the real kernel
> in "a0" before jumping to it.
>
> Signed-off-by: Atish Patra <atish.patra at wdc.com>
> ---
>  arch/riscv/lib/bootm.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/arch/riscv/lib/bootm.c b/arch/riscv/lib/bootm.c
> index fad16901c5f2..b84cc2db2016 100644
> --- a/arch/riscv/lib/bootm.c
> +++ b/arch/riscv/lib/bootm.c
> @@ -28,6 +28,19 @@ __weak void board_quiesce_devices(void)
>
>  int arch_fixup_fdt(void *blob)
>  {
> +       u32 size;
> +       int chosen_offset, err;
> +
> +       size = fdt_totalsize(blob);
> +       err  = fdt_open_into(blob, blob, size + 32);
> +       if (err < 0) {
> +               printf("Device Tree can't be expanded to accmodate new node");

'accommodate'

> +               return -1;
> +       }
> +       chosen_offset = fdt_path_offset(blob, "/chosen");
> +       fdt_setprop_u64(blob, chosen_offset, "efi-boot-hartid",

I assume that boot hartid does not change value when you boot via
UEFI, so this should simply be /chosen/boot-hartid

> +                          gd->arch.boot_hart);
> +
>         return 0;
>  }
>
> --
> 2.24.0
>