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

[Luca Fancellu <Luca.Fancellu@arm.com>]

Hi Julien,

> On 6 May 2025, at 12:44, Julien Grall <julien@xen.org> wrote:
> 
> 
> 
> 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@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.
> 
> 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

Just to be sure to be on the same page, are you suggesting these changes on the original file?

diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
index 21ae74837dcc..c00c651805d7 100644
--- a/docs/misc/arm/booting.txt
+++ b/docs/misc/arm/booting.txt
@@ -58,10 +58,14 @@ Firmware/bootloader requirements
 
 Xen relies on some settings the firmware has to configure in EL3 before starting Xen.
 
-* Xen must be entered in NS EL2 mode
+* Xen must be entered in:
+  * Non-Secure EL2 mode for Armv8-A Arm64 and Arm32, Armv8-R Arm32.
+  * Secure EL2 mode for Armv8-R Arm64.
 
 * The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.
 
+* Xen must be entered with MMU/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

Cheers,
Luca