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

[Luca Fancellu <luca.fancellu@xxxxxxx>]

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.
+
+* 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
-- 
2.34.1