[PATCH v2] dt-bindings: riscv: Add SiFive vendor extensions description

[Nick Hu <nick.hu@sifive.com>]

Add description for SiFive vendor extensions "xsfcflushdlone",
"xsfpgflushdlone" and "xsfcease". This is used in the SBI
implementation [1].

[1] https://lore.kernel.org/opensbi/20250708074940.10904-1-nick.hu@sifive.com/

Changes in v2:
- Update the message to indicate the user of the extensions.

Signed-off-by: Nick Hu <nick.hu@sifive.com>
---
 .../devicetree/bindings/riscv/extensions.yaml  | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
index ede6a58ccf53..5638297759df 100644
--- a/Documentation/devicetree/bindings/riscv/extensions.yaml
+++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
@@ -663,6 +663,24 @@ properties:
             https://www.andestech.com/wp-content/uploads/AX45MP-1C-Rev.-5.0.0-Datasheet.pdf
 
         # SiFive
+        - const: xsfcease
+          description:
+            SiFive CEASE Instruction Extensions Specification.
+            See more details in
+            https://www.sifive.com/document-file/freedom-u740-c000-manual
+
+        - const: xsfcflushdlone
+          description:
+            SiFive L1D Cache Flush Instruction Extensions Specification.
+            See more details in
+            https://www.sifive.com/document-file/freedom-u740-c000-manual
+
+        - const: xsfpgflushdlone
+          description:
+            SiFive PGFLUSH Instruction Extensions for the power management. The
+            CPU will flush the L1D and enter the cease state after executing
+            the instruction.
+
         - const: xsfvqmaccdod
           description:
             SiFive Int8 Matrix Multiplication Extensions Specification.
-- 
2.17.1