scsi: ufs: dt-bindings: Document gear and rate limit properties

Add optional "limit-hs-gear" and "limit-rate" properties to the UFS
controller common binding. These properties allow limiting the maximum
HS gear and rate.

This is useful in cases where the customer board may have signal
integrity, clock configuration or layout issues that prevent reliable
operation at higher gears. Such limitations are especially critical in
those platforms, where stability is prioritized over peak performance.

Reviewed-by: Krzysztof Kozlowski <[email protected]>
Signed-off-by: Ram Kumar Dwivedi <[email protected]>
Reviewed-by: Alim Akhtar <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: Ram Kumar Dwivedi

Documentation/devicetree/bindings/ufs/ufs-common.yaml

@@ -89,6 +89,22 @@ properties:
 
   msi-parent: true
 
+  limit-hs-gear:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 1
+    maximum: 6
+    default: 6
+    description:
+      Restricts the maximum HS gear used in both TX and RX directions.
+
+  limit-gear-rate:
+    $ref: /schemas/types.yaml#/definitions/string
+    enum: [rate-a, rate-b]
+    default: rate-b
+    description:
+      Restricts the UFS controller to rate-a or rate-b for both TX and
+      RX directions.
+
 dependencies:
   freq-table-hz: [ clocks ]
   operating-points-v2: [ clocks, clock-names ]