[PATCH v5 1/6] riscv: Add boot hartid to Device tree

[Heinrich Schuchardt]

On 4/6/20 10:44 PM, Atish Patra wrote:
> Linux booting protocol mandates that register "a0" contains the hartid.
> However, U-boot can not pass the hartid via a0 during via standard UEFI
> protocol. DT nodes are commonly used to pass such information to the OS.
>
> 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>
> Reviewed-by: Rick Chen <rick at andestech.com>
> ---
>  arch/riscv/lib/bootm.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/arch/riscv/lib/bootm.c b/arch/riscv/lib/bootm.c
> index fad16901c5f2..87cadad5016d 100644
> --- a/arch/riscv/lib/bootm.c
> +++ b/arch/riscv/lib/bootm.c
> @@ -28,6 +28,28 @@ __weak void board_quiesce_devices(void)
>
>  int arch_fixup_fdt(void *blob)
>  {
> +#ifdef CONFIG_EFI_LOADER
> +	int err;
> +	u32 size;
> +	int chosen_offset;
> +
> +	size = fdt_totalsize(blob);
> +	err  = fdt_open_into(blob, blob, size + 32);
> +	if (err < 0) {
> +		printf("Device Tree can't be expanded to accommodate new node");
> +		return err;
> +	}
> +	chosen_offset = fdt_path_offset(blob, "/chosen");
> +	if (chosen_offset < 0) {
> +		err = fdt_add_subnode(blob, 0, "chosen");
> +		if (err < 0) {
> +			printf("chosen node can not be added\n");
> +			return err;
> +		}
> +	}
> +	/* Overwrite the boot-hartid as U-Boot is the last stage BL */
> +	fdt_setprop_u32(blob, chosen_offset, "boot-hartid", gd->arch.boot_hart);
> +#endif
>  	return 0;
>  }
>
>

I have tested this on qemu-riscv64_defconfig by comparing the device
tree before and after running helloworld.efi:

=> fdt addr $fdtcontroladdr
=> fdt print /chosen
chosen {
        bootargs = "";
        stdout-path = "/uart at 10000000";
};
...
=> dhcp $kernel_addr_r helloworld.efi
=> bootefi $kernel_addr_r
...
=> fdt addr 0x87F00000
=> fdt print /chosen
chosen {
        riscv,kernel-end = <0x00000000 0x00000000>;
        riscv,kernel-start = <0x00000000 0x00000000>;
        boot-hartid = <0x00000000>;
        bootargs = "";
        stdout-path = "/uart at 10000000";
};

The entry for boot-hardid seems to be ok.

But the riscv,kernel-end and riscv,kernel-start values are just some
dummy values introduced in:

board/emulation/qemu-riscv/qemu-riscv.c:84
commit 897206c5cc5c ("riscv: qemu: clear kernel-start/-end in device
tree as workaround for BBL)"

@Lukas:
Why are these values set to zero and not deleted (using fdt_delprop())
from the device tree? I cannot see that we need them when booting via UEFI.

Tested-by: Heinrich Schuchardt <xypron.glpk at gmx.de>