Re: [PATCH v4 1/2] dt-bindings: rtc: Add property for Raspberry Pi 5 RTC

[Conor Dooley <conor@kernel.org>]

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On Wed, Sep 23, 2026 at 03:13:22PM +0200, Sander Speetjens wrote:
> 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.
> 
> Signed-off-by: Sander Speetjens <sander.speetjens@gmail.com>
> ---
> V3 -> V4: Add a reff to uint32
> 
> V2 -> V3: Fixed the firmware property naming
> 
> V1 -> V2: As discussed with Krzysztof Kozlowski, this property is folded into
> the existing raspberrypi,bcm2835-firmware properties.
> 
>  .../bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml    | 8 ++++++++
>  1 file changed, 8 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..9349fc8908a5 100644
> --- a/Documentation/devicetree/bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml
> +++ b/Documentation/devicetree/bindings/arm/bcm/raspberrypi,bcm2835-firmware.yaml
> @@ -133,6 +133,13 @@ properties:
>      required:
>        - compatible
>  
> +  trickle-voltage-millivolt:
> +    allOf:
> +      - $ref: /schemas/rtc/rtc.yaml#/properties/trickle-voltage-millivolt
> +      - $ref: /schemas/types.yaml#/definitions/uint32

Is this actually needed? Shouldn't the type of uint32 come from the same
source that the type in rtc.yaml does? Or is this missing in dt-schema?

> +      - minimum: 1300
> +        maximum: 5000
> +
>  required:
>    - compatible
>    - mboxes
> @@ -144,6 +151,7 @@ examples:
>      firmware {
>          compatible = "raspberrypi,bcm2835-firmware", "simple-mfd";
>          mboxes = <&mailbox>;
> +        trickle-voltage-millivolt = <3300>;
>  
>          firmware_clocks: clocks {
>              compatible = "raspberrypi,firmware-clocks";
> -- 
> 2.55.0
> 

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