[RFC PATCH 0/1] Add boot hartid to a Device tree

[Heinrich Schuchardt]

On 2/24/20 11:19 PM, Atish Patra wrote:
> The RISC-V booting protocol requires the hart id to be present in "a0"
> register. This is not a problem for bootm/booti commands as they directly
> jump to Linux kernel. However, bootefi jumps to a EFI boot stub code in
> Linux kernel which acts a loader and jumps to real Linux after terminating
> the boot services. This boot stub code has to be aware of the boot hart id
> so that it can set it in "a0" before jumping to Linux kernel. Currently,
> UEFI protocol doesn't have any mechanism to pass the boot hart id to an
> EFI executable. We should keep it this way as this is a RISC-V specific
> requirement rather than a UEFI requirement. Out of the all possible options,
> device tree seemed to be the best choice to do this job.
> The detailed discussion can be found in the following thread.
>
> https://patchwork.ozlabs.org/patch/1233664/

The above mentioned patch is obsoleted by the new suggestion.

>
> This patch updates the device tree in arch_fixup_fdt() which is common for
> all booting commands. As a result, the DT modification doesn't require any
> efi related arch specific functions and all DT related modifications are
> contained at one place. However, the hart id node will be available for
> Linux even if the kernel is booted using bootm command.
>
> If that is not acceptable, we can always move the code to an efi specific
> function.

Does a related Linux patch already exist?
How about EDK2?

I guess boot loaders like GRUB would not have to care about the extra
property?

Best regards

Heinrich

>
> Atish Patra (1):
> riscv: Add boot hartid to Device tree
>
> arch/riscv/lib/bootm.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> --
> 2.24.0
>