Add ref-sync-sources phandle-array property to the dpll-pin schema
allowing board designers to declare which input pins can serve as
sync sources in a Reference-Sync pair.  A Ref-Sync pair consists of
a clock reference and a low-frequency sync signal where the DPLL locks
to the clock but phase-aligns to the sync reference.

Update both examples in the Microchip ZL3073x binding to demonstrate
the new property with a 1 PPS sync source paired to a clock source.

Reviewed-by: Petr Oros <poros@redhat.com>
Reviewed-by: Prathosh Satish <Prathosh.Satish@microchip.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
 .../devicetree/bindings/dpll/dpll-pin.yaml    | 11 +++++++
 .../bindings/dpll/microchip,zl30731.yaml      | 30 ++++++++++++++-----
 2 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/Documentation/devicetree/bindings/dpll/dpll-pin.yaml b/Documentation/devicetree/bindings/dpll/dpll-pin.yaml
index 51db93b77306f..7084f102e274c 100644
--- a/Documentation/devicetree/bindings/dpll/dpll-pin.yaml
+++ b/Documentation/devicetree/bindings/dpll/dpll-pin.yaml
@@ -36,6 +36,17 @@ properties:
     description: String exposed as the pin board label
     $ref: /schemas/types.yaml#/definitions/string
 
+  ref-sync-sources:
+    description: |
+      List of phandles to input pins that can serve as the sync source
+      in a Reference-Sync pair with this pin acting as the clock source.
+      A Ref-Sync pair consists of a clock reference and a low-frequency
+      sync signal.  The DPLL locks to the clock reference but
+      phase-aligns to the sync reference.
+      Only valid for input pins.  Each referenced pin must be a
+      different input pin on the same device.
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+
   supported-frequencies-hz:
     description: List of supported frequencies for this pin, expressed in Hz.
 
diff --git a/Documentation/devicetree/bindings/dpll/microchip,zl30731.yaml b/Documentation/devicetree/bindings/dpll/microchip,zl30731.yaml
index 17747f754b845..fa5a8f8e390cd 100644
--- a/Documentation/devicetree/bindings/dpll/microchip,zl30731.yaml
+++ b/Documentation/devicetree/bindings/dpll/microchip,zl30731.yaml
@@ -52,11 +52,19 @@ examples:
           #address-cells = <1>;
           #size-cells = <0>;
 
-          pin@0 { /* REF0P */
+          sync0: pin@0 { /* REF0P - 1 PPS sync source */
             reg = <0>;
             connection-type = "ext";
-            label = "Input 0";
-            supported-frequencies-hz = /bits/ 64 <1 1000>;
+            label = "SMA1";
+            supported-frequencies-hz = /bits/ 64 <1>;
+          };
+
+          pin@1 { /* REF0N - clock source, can pair with sync0 */
+            reg = <1>;
+            connection-type = "ext";
+            label = "SMA2";
+            supported-frequencies-hz = /bits/ 64 <10000 10000000>;
+            ref-sync-sources = <&sync0>;
           };
         };
 
@@ -90,11 +98,19 @@ examples:
           #address-cells = <1>;
           #size-cells = <0>;
 
-          pin@0 { /* REF0P */
+          sync1: pin@0 { /* REF0P - 1 PPS sync source */
             reg = <0>;
-            connection-type = "ext";
-            label = "Input 0";
-            supported-frequencies-hz = /bits/ 64 <1 1000>;
+            connection-type = "gnss";
+            label = "GNSS_1PPS_IN";
+            supported-frequencies-hz = /bits/ 64 <1>;
+          };
+
+          pin@1 { /* REF0N - clock source */
+            reg = <1>;
+            connection-type = "gnss";
+            label = "GNSS_10M_IN";
+            supported-frequencies-hz = /bits/ 64 <10000000>;
+            ref-sync-sources = <&sync1>;
           };
         };
 
-- 
2.52.0