linux-kernel - Re: [PATCH 1/3] dt-bindings: rtc: Add Apple SMC RTC

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Message-Id: <87wm78l6xy.fsf@bloch.sibelius.xs4all.nl>
Date: Tue, 12 Aug 2025 20:40:25 +0200
From: Mark Kettenis <mark.kettenis@...all.nl>
To: Sven Peter <sven@...nel.org>
Cc: j@...nau.net, alyssa@...enzweig.io, neal@...pa.dev,
	lee@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, alexandre.belloni@...tlin.com,
	asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-rtc@...r.kernel.org, sven@...nel.org
Subject: Re: [PATCH 1/3] dt-bindings: rtc: Add Apple SMC RTC

> From: Sven Peter <sven@...nel.org>
> Date: Tue, 12 Aug 2025 18:25:15 +0000
> 
> Apple Silicon Macs (M1, etc.) have an RTC that is part of the PMU IC,
> but most of the PMU functionality is abstracted out by the SMC.
> An additional RTC offset stored inside NVMEM is required to compute
> the current date/time.
> 
> Signed-off-by: Sven Peter <sven@...nel.org>

Reviewd-by: Mark Kettenis <kettenis@...nbsd.org>

> ---
>  .../devicetree/bindings/mfd/apple,smc.yaml         |  9 ++++++
>  .../devicetree/bindings/rtc/apple,smc-rtc.yaml     | 35 ++++++++++++++++++++++
>  MAINTAINERS                                        |  1 +
>  3 files changed, 45 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mfd/apple,smc.yaml b/Documentation/devicetree/bindings/mfd/apple,smc.yaml
> index 8a10e270d421ecd703848f64af597de351fcfd74..38f077867bdeedba8a486a63e366e9c943a75681 100644
> --- a/Documentation/devicetree/bindings/mfd/apple,smc.yaml
> +++ b/Documentation/devicetree/bindings/mfd/apple,smc.yaml
> @@ -41,6 +41,9 @@ properties:
>    reboot:
>      $ref: /schemas/power/reset/apple,smc-reboot.yaml
>  
> +  rtc:
> +    $ref: /schemas/rtc/apple,smc-rtc.yaml
> +
>  additionalProperties: false
>  
>  required:
> @@ -75,5 +78,11 @@ examples:
>            nvmem-cell-names = "shutdown_flag", "boot_stage",
>                               "boot_error_count", "panic_count";
>          };
> +
> +        rtc {
> +          compatible = "apple,smc-rtc";
> +          nvmem-cells = <&rtc_offset>;
> +          nvmem-cell-names = "rtc_offset";
> +       };
>        };
>      };
> diff --git a/Documentation/devicetree/bindings/rtc/apple,smc-rtc.yaml b/Documentation/devicetree/bindings/rtc/apple,smc-rtc.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..607b610665a28b3ea2e86bd90cb5f3f28ebac726
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/rtc/apple,smc-rtc.yaml
> @@ -0,0 +1,35 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/rtc/apple,smc-rtc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Apple SMC RTC
> +
> +description:
> +  Apple Silicon Macs (M1, etc.) have an RTC that is part of the PMU IC,
> +  but most of the PMU functionality is abstracted out by the SMC.
> +  An additional RTC offset stored inside NVMEM is required to compute
> +  the current date/time.
> +
> +maintainers:
> +  - Sven Peter <sven@...nel.org>
> +
> +properties:
> +  compatible:
> +    const: apple,smc-rtc
> +
> +  nvmem-cells:
> +    items:
> +      - description: 48bit RTC offset, specified in 32768 (2^15) Hz clock ticks
> +
> +  nvmem-cell-names:
> +    items:
> +      - const: rtc_offset
> +
> +required:
> +  - compatible
> +  - nvmem-cells
> +  - nvmem-cell-names
> +
> +additionalProperties: false
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fe168477caa45799dfe07de2f54de6d6a1ce0615..aaef8634985b35f54de1123ebb4176602066d177 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2397,6 +2397,7 @@ F:	Documentation/devicetree/bindings/pinctrl/apple,pinctrl.yaml
>  F:	Documentation/devicetree/bindings/power/apple*
>  F:	Documentation/devicetree/bindings/power/reset/apple,smc-reboot.yaml
>  F:	Documentation/devicetree/bindings/pwm/apple,s5l-fpwm.yaml
> +F:	Documentation/devicetree/bindings/rtc/apple,smc-rtc.yaml
>  F:	Documentation/devicetree/bindings/spi/apple,spi.yaml
>  F:	Documentation/devicetree/bindings/spmi/apple,spmi.yaml
>  F:	Documentation/devicetree/bindings/watchdog/apple,wdt.yaml
> 
> -- 
> 2.34.1
> 
> 
> 
>