[PATCH 2/3] spi: dt-bindings: Add num-cs property for mpfs-spi

[Prajna Rajendra Kumar <prajna.rajendrakumar@microchip.com>]

The PolarFire SoC SPI controller supports multiple chip selects,but in
the MSS, only one CS line is physically wired. To reflect this hardware
limitation in the device tree, the binding enforces that the 'num-cs'
property defaults to 1 and cannot exceed 1 unless additional
chip select lines are explicitly defined using GPIO descriptors.

Fixes: 2da187304e55 ("spi: add bindings for microchip mpfs spi")
Signed-off-by: Prajna Rajendra Kumar <prajna.rajendrakumar@microchip.com>
---
 .../bindings/spi/microchip,mpfs-spi.yaml      | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/spi/microchip,mpfs-spi.yaml b/Documentation/devicetree/bindings/spi/microchip,mpfs-spi.yaml
index 74a817cc7d94..19951951fdd6 100644
--- a/Documentation/devicetree/bindings/spi/microchip,mpfs-spi.yaml
+++ b/Documentation/devicetree/bindings/spi/microchip,mpfs-spi.yaml
@@ -13,9 +13,6 @@ description:
 maintainers:
   - Conor Dooley <conor.dooley@microchip.com>
 
-allOf:
-  - $ref: spi-controller.yaml#
-
 properties:
   compatible:
     oneOf:
@@ -43,6 +40,22 @@ required:
   - interrupts
   - clocks
 
+allOf:
+  - $ref: spi-controller.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: microchip,mpfs-spi
+      not:
+        required:
+          - cs-gpios
+    then:
+      properties:
+        num-cs:
+          default: 1
+          maximum: 1
+
 unevaluatedProperties: false
 
 examples:
-- 
2.25.1