[PATCH v14 2/3] dt-bindings: rtc: Add property for Raspberry Pi 5 RTC

[Sander Speetjens]

The Raspberry Pi 5 has a built-in RTC that can be battery-backed
via the VBAT pin. When a rechargeable coin cell is used, the
hardware requires a trickle-charge voltage to keep the battery
topped up.

Expose the trickle-voltage-millivolt DT property so the driver can
program the correct charge voltage for board specific configurations with
the attached battery.

The property is added to the existing raspberrypi,bcm2835-firmware
binding (rather than creating a new RTC node) because the RTC is
accessed exclusively through the firmware mailbox interface.
We only $ref the individual property from rtc.yaml and do not
reference the full schema, because the firmware node name does not
match the $nodename pattern required by rtc.yaml.

Acked-by: Conor Dooley <conor.dooley at microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski at oss.qualcomm.com>
Signed-off-by: Sander Speetjens <sander.speetjens at gmail.com>
---
V13 -> V14: No changes

V13: https://lore.kernel.org/linux-rtc/20261018150028.1047172-1-sander.speetjens@gmail.com

 .../bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml      | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml b/Documentation/devicetree/bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml
index 983ea80eaec9..dc71fd57834e 100644
--- a/Documentation/devicetree/bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml
+++ b/Documentation/devicetree/bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml
@@ -133,6 +133,11 @@ properties:
     required:
       - compatible
 
+  trickle-voltage-millivolt:
+    $ref: /schemas/rtc/rtc.yaml#/properties/trickle-voltage-millivolt
+    minimum: 1300
+    maximum: 5000
+
 required:
   - compatible
   - mboxes
@@ -144,6 +149,7 @@ examples:
     firmware {
         compatible = "raspberrypi,bcm2835-firmware", "simple-mfd";
         mboxes = <&mailbox>;
+        trickle-voltage-millivolt = <3300>;
 
         firmware_clocks: clocks {
             compatible = "raspberrypi,firmware-clocks";
-- 
2.56.0