[RFC PATCH 24/36] arm64: booting: Document boot requirements for FEAT_NMI

[Vladimir Murzin <vladimir.murzin@arm.com>]

From: Mark Brown <broonie@kernel.org>

In order to use FEAT_NMI we must be able to use ALLINT, require that
it behave as though not trapped when it is present.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
 Documentation/arch/arm64/booting.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst
index 13ef311dace8..3170b26ae981 100644
--- a/Documentation/arch/arm64/booting.rst
+++ b/Documentation/arch/arm64/booting.rst
@@ -568,6 +568,12 @@ Before jumping into the kernel, the following conditions must be met:
 
     - HCRX_EL2.EnASR (bit 2) must be initialised to 0b1.
 
+  For CPUs with support for Non-maskable Interrupts (FEAT_NMI):
+
+  - If the kernel is entered at EL1 and EL2 is present:
+
+    - HCRX_EL2.TALLINT (bit 6) must be initialised to 0b0.
+
 The requirements described above for CPU mode, caches, MMUs, architected
 timers, coherency and system registers apply to all CPUs.  All CPUs must
 enter the kernel in the same exception level.  Where the values documented
-- 
2.34.1