[xen staging] SUPPORT.md: Describe SCMI-SMC layer feature

[patchbot@xxxxxxx]

commit 294faa3760bd40c1084f5bcc6c213e2e64c64dae
Author:     Andrei Cherechesu <andrei.cherechesu@xxxxxxx>
AuthorDate: Thu Dec 19 13:23:14 2024 +0200
Commit:     Michal Orzel <michal.orzel@xxxxxxx>
CommitDate: Thu Dec 19 19:26:21 2024 +0100

    SUPPORT.md: Describe SCMI-SMC layer feature
    
    Describe the layer which enables SCMI over SMC calls forwarding
    to EL3 FW if issued by the Hardware domain. If the SCMI firmware
    node is not found in the Host DT during initialization, it fails
    silently as it's not mandatory.
    
    The SCMI SMCs trapping at EL2 now lets hwdom perform SCMI ops for
    interacting with system-level resources almost as if it would be
    running natively.
    
    Signed-off-by: Andrei Cherechesu <andrei.cherechesu@xxxxxxx>
    Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
    Acked-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 SUPPORT.md | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/SUPPORT.md b/SUPPORT.md
index 998faf5635..54c78b722d 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -935,6 +935,14 @@ Add/Remove device tree nodes using a device tree overlay 
binary (.dtbo).
 
     Status: Tech Preview
 
+### Arm: SCMI over SMC calls forwarding to EL3 Firmware
+
+Enable SCMI calls using SMC as doorbell mechanism and Shared Memory for
+transport ("arm,scmi-smc" compatible only) to reach EL3 Firmware if issued
+by hwdom. Some platforms use SCMI for access to system-level resources.
+
+    Status: Supported
+
 ## Virtual Hardware, QEMU
 
 This section describes supported devices available in HVM mode using a
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