dt-bindings: rtc: stm32: describe pinmux nodes

STM32 RTC is capable to handle 3 specific pins of the soc (out1, out2,
out2_rmp) and to outputs 2 signals (LSCO, alarm-a).

This feature is configured thanks to pinmux nodes and pinctrl framework.
This feature is available with compatible st,stm32mp1-rtc and
st,stm32mp25-rtc only.

Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240722160022.454226-2-valentin.caron@foss.st.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Documentation/devicetree/bindings/rtc/st,stm32-rtc.yaml

@@ -53,6 +53,28 @@ properties:
       override default rtc_ck parent clock phandle of the new parent clock of rtc_ck
     maxItems: 1
 
+patternProperties:
+  "^rtc-[a-z]+-[0-9]+$":
+    type: object
+    $ref: /schemas/pinctrl/pinmux-node.yaml
+    description: |
+      Configuration of STM32 RTC pins description. STM32 RTC is able to output
+      some signals on specific pins:
+      - LSCO (Low Speed Clock Output) that allow to output LSE clock on a pin.
+      - Alarm out that allow to send a pulse on a pin when alarm A of the RTC
+        expires.
+    additionalProperties: false
+    properties:
+      function:
+        enum:
+          - lsco
+          - alarm-a
+      pins:
+        enum:
+          - out1
+          - out2
+          - out2_rmp
+
 allOf:
   - if:
       properties:
@@ -68,6 +90,9 @@ allOf:
 
         clock-names: false
 
+      patternProperties:
+        "^rtc-[a-z]+-[0-9]+$": false
+
       required:
         - st,syscfg
 
@@ -83,6 +108,9 @@ allOf:
           minItems: 2
           maxItems: 2
 
+      patternProperties:
+        "^rtc-[a-z]+-[0-9]+$": false
+
       required:
         - clock-names
         - st,syscfg