Re: [PATCH] xen/arm64: head: document missing input registers for MMU functions

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 30/05/2025 22:31, Mykola Kvach wrote:
> From: Mykola Kvach <mykola_kvach@xxxxxxxx>
> 
> Add missing input register descriptions to enable_secondary_cpu_mm
> and enable_boot_cpu_mm functions.
> 
> Specifically:
> - x19 is used in enable_boot_cpu_mm as physical start address.
> - x20 is used in both functions for physical offset passed to load_paddr.
I'm not sure if we need to document register usage that is part of a comment in
so called "Common register usage". It's repeating information for me. That said,
I can see that Arm32 does that too so no objection.

> 
> This update improves code clarity and consistency in comments.
> 
> No functional changes are introduced by this patch.
> 
> Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
> ---
>  xen/arch/arm/arm64/mmu/head.S | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/xen/arch/arm/arm64/mmu/head.S b/xen/arch/arm/arm64/mmu/head.S
> index 634156f83d..033b3a018a 100644
> --- a/xen/arch/arm/arm64/mmu/head.S
> +++ b/xen/arch/arm/arm64/mmu/head.S
> @@ -313,6 +313,7 @@ END(enable_mmu)
>   *
>   * Inputs:
>   *   lr : Virtual address to return to.
> + *   x20: phys offset (used by load_paddr)
>   *
>   * Clobbers x0 - x6
>   */
> @@ -337,6 +338,8 @@ END(enable_secondary_cpu_mm)
>   *
>   * Inputs:
>   *   lr : Virtual address to return to.
> + *   x19: paddr(start) (used by remove_identity_mapping)
AFAICT it's also used by create_page_tables. I don't see it beneficial to
mention the places the register is used. It can easily go stale.

With the remark addressed:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal