linux-kernel - [PATCH v5 01/11] dt-bindings: rtc: Add Apple SMC RTC

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Message-Id: <20251112-macsmc-subdevs-v5-1-728e4b91fe81@gmail.com>
Date: Wed, 12 Nov 2025 21:16:47 +1000
From: James Calligeros <jcalligeros99@...il.com>
To: Sven Peter <sven@...nel.org>, Janne Grunau <j@...nau.net>, 
 Alyssa Rosenzweig <alyssa@...enzweig.io>, Neal Gompa <neal@...pa.dev>, 
 Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>, 
 Dmitry Torokhov <dmitry.torokhov@...il.com>, 
 Jonathan Corbet <corbet@....net>, 
 James Calligeros <jcalligeros99@...il.com>
Cc: asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-rtc@...r.kernel.org, linux-hwmon@...r.kernel.org, 
 linux-input@...r.kernel.org, linux-doc@...r.kernel.org, 
 Mark Kettenis <kettenis@...nbsd.org>
Subject: [PATCH v5 01/11] dt-bindings: rtc: Add Apple SMC RTC

From: Sven Peter <sven@...nel.org>

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.

Reviewed-by: Mark Kettenis <kettenis@...nbsd.org>
Reviewed-by: Neal Gompa <neal@...pa.dev>
Reviewed-by: Rob Herring (Arm) <robh@...nel.org>
Signed-off-by: Sven Peter <sven@...nel.org>
Signed-off-by: James Calligeros <jcalligeros99@...il.com>
---
 .../bindings/mfd/apple,smc.yaml          |  9 +++++++
 .../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 5429538f7e2e..0410e712c900 100644
--- a/Documentation/devicetree/bindings/mfd/apple,smc.yaml
+++ b/Documentation/devicetree/bindings/mfd/apple,smc.yaml
@@ -46,6 +46,9 @@ properties:
   reboot:
     $ref: /schemas/power/reset/apple,smc-reboot.yaml
 
+  rtc:
+    $ref: /schemas/rtc/apple,smc-rtc.yaml
+
 additionalProperties: false
 
 required:
@@ -80,5 +83,11 @@ 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 000000000000..607b610665a2
--- /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 f0c8b85baa6b..51942a9a9b43 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2439,6 +2439,7 @@ 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

-- 
2.51.2