dt-bindings: riscv: Add Supm extension description

Add description for the Supm extension. Supm indicates support for pointer
masking in user mode. Supm is mandatory for RVA23S64.

Add dependency check that Supm requires either Smnpm or Ssnpm.

The Supm extension is ratified in commit d70011dde6c2 ("Update to ratified
state") of riscv-j-extension.

Signed-off-by: Guodong Xu <guodong@riscstar.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Documentation/devicetree/bindings/riscv/extensions.yaml

@@ -262,6 +262,23 @@ properties:
             ratified in RISC-V Profiles Version 1.0, with commit b1d806605f87
             ("Updated to ratified state.")
 
+        - const: supm
+          description: |
+            The standard Supm extension for pointer masking support in user
+            mode (U-mode) as ratified at commit d70011dde6c2 ("Update to
+            ratified state") of riscv-j-extension.
+
+            Supm represents a combination of underlying hardware capability
+            (Smnpm or Ssnpm), U-mode consumer privilege level, and M/S-mode
+            software configuration that enables pointer masking for U-mode.
+
+            DO NOT include this property in device trees targeting privileged
+            system software (S-mode or M-mode).
+
+            This property is only appropriate in device trees provided to
+            U-mode software where the next-higher-privilege-mode supports
+            Smnpm or Ssnpm and enables it for U-mode.
+
         - const: svade
           description: |
             The standard Svade supervisor-level extension for SW-managed PTE A/D
@@ -907,6 +924,16 @@ properties:
         then:
           contains:
             const: b
+      # Supm depends on Smnpm or Ssnpm
+      - if:
+          contains:
+            const: supm
+        then:
+          oneOf:
+            - contains:
+                const: smnpm
+            - contains:
+                const: ssnpm
       # Za64rs and Ziccrse depend on Zalrsc or A
       - if:
           contains: