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

[Julien Grall <julien@xxxxxxx>]

On 29/04/2025 16:20, Luca Fancellu wrote:
> Document the requirement needed to boot Xen on Armv8-R platforms.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> 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.
I think it would be better to update the line "Xen must be entered in NS 
EL2 mode" to clarify the state for 64-bit Arm.
> +> +* Xen must be entered with MPU off and data cache disabled 
(SCTLR_EL2.M bit and
> +  SCTLR_EL2.C set to 0).
This line is valid for Armv8-A/Armv7-A when using the Image/zImage protocol.

>   
>   [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
--
Julien Grall