Re: [PATCH v4 1/7] docs/arm: Document Xen booting protocol on Armv8-R

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

On 29/04/2025 17:20, Luca Fancellu wrote:
> Document the requirement needed to boot Xen on Armv8-R platforms.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
> ---
> v4 changes:
>  - New patch
> ---
>  docs/misc/arm/booting.txt | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
> index 21ae74837dcc..719af74f1e69 100644
> --- a/docs/misc/arm/booting.txt
> +++ b/docs/misc/arm/booting.txt
> @@ -62,6 +62,14 @@ Xen relies on some settings the firmware has to configure in EL3 before starting
>  
>  * The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.
>  
> +When Xen runs on Armv8-R, the highest exception level is EL2 and the only
> +available state is secure (S) on Arm64 and non secure (NS) on Arm32, hence the
> +above requirements need to be adjusted to this case:
> +
> +* Xen must be entered in S EL2 mode on Arm64 and in NS EL2 mode on Arm32.
> +
> +* Xen must be entered with MPU off and data cache disabled (SCTLR_EL2.M bit and
> +  SCTLR_EL2.C set to 0).
>  
>  [1] linux/Documentation/arm/booting.rst
>  Latest version: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/arch/arm/booting.rst

Is the goal of this patch to only write firmware/bootloader requirements or
accommodate booting protocol in general? Asking because in this file there is a
requirement that Xen should be loaded below 10TB which afaict does not fit Armv8-R.

Other than that:
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

~Michal