linux-kernel - Re: [PATCH v4 03/11] rtc: Add new rtc-macsmc driver for Apple Silicon Macs

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Message-ID: <20251106135414.GO8064@google.com>
Date: Thu, 6 Nov 2025 13:54:14 +0000
From: Lee Jones <lee@...nel.org>
To: James Calligeros <jcalligeros99@...il.com>
Cc: Sven Peter <sven@...nel.org>, Janne Grunau <j@...nau.net>,
	Alyssa Rosenzweig <alyssa@...enzweig.io>,
	Neal Gompa <neal@...pa.dev>, 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>, 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, Hector Martin <marcan@...can.st>
Subject: Re: [PATCH v4 03/11] rtc: Add new rtc-macsmc driver for Apple
 Silicon Macs

On Sat, 25 Oct 2025, James Calligeros wrote:

> From: Hector Martin <marcan@...can.st>
> 
> 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.
> On T600x machines, the RTC counter must be accessed via the SMC to
> get full functionality, and it seems likely that future machines
> will move towards making SMC handle all RTC functionality.
> 
> The SMC RTC counter access is implemented on all current machines
> as of the time of this writing, on firmware 12.x. However, the RTC
> offset (needed to set the time) is still only accessible via direct
> PMU access. To handle this, we expose the RTC offset as an NVMEM
> cell from the SPMI PMU device node, and this driver consumes that
> cell and uses it to compute/set the current time.
> 
> Reviewed-by: Neal Gompa <neal@...pa.dev>
> Signed-off-by: Hector Martin <marcan@...can.st>
> Signed-off-by: Sven Peter <sven@...nel.org>
> Signed-off-by: James Calligeros <jcalligeros99@...il.com>
> ---
>  MAINTAINERS              |   1 +
>  drivers/rtc/Kconfig      |  11 ++
>  drivers/rtc/Makefile     |   1 +
>  drivers/rtc/rtc-macsmc.c | 141 +++++++++++++++++++++++++
>  4 files changed, 154 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 10f4c0034b5e..3c6322872dd1 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2460,6 +2460,7 @@ F:	drivers/nvmem/apple-spmi-nvmem.c
>  F:	drivers/pinctrl/pinctrl-apple-gpio.c
>  F:	drivers/power/reset/macsmc-reboot.c
>  F:	drivers/pwm/pwm-apple.c
> +F:	drivers/rtc/rtc-macsmc.c
>  F:	drivers/soc/apple/*
>  F:	drivers/spi/spi-apple.c
>  F:	drivers/spmi/spmi-apple-controller.c
> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> index 4a8dc8d0a4b7..e165301d4abb 100644
> --- a/drivers/rtc/Kconfig
> +++ b/drivers/rtc/Kconfig
> @@ -2078,6 +2078,17 @@ config RTC_DRV_WILCO_EC
>  	  This can also be built as a module. If so, the module will
>  	  be named "rtc_wilco_ec".
>  
> +config RTC_DRV_MACSMC
> +	tristate "Apple Mac System Management Controller RTC"
> +	depends on MFD_MACSMC
> +	help
> +	  If you say yes here you get support for RTC functions
> +	  inside Apple SPMI PMUs accessed through the SoC's
> +	  System Management Controller
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called rtc-macsmc.
> +
>  config RTC_DRV_MSC313
>  	tristate "MStar MSC313 RTC"
>          depends on ARCH_MSTARV7 || COMPILE_TEST
> diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
> index 610a9ee5fd33..32083bd5bb81 100644
> --- a/drivers/rtc/Makefile
> +++ b/drivers/rtc/Makefile
> @@ -93,6 +93,7 @@ obj-$(CONFIG_RTC_DRV_M48T35)	+= rtc-m48t35.o
>  obj-$(CONFIG_RTC_DRV_M48T59)	+= rtc-m48t59.o
>  obj-$(CONFIG_RTC_DRV_M48T86)	+= rtc-m48t86.o
>  obj-$(CONFIG_RTC_DRV_MA35D1)	+= rtc-ma35d1.o
> +obj-$(CONFIG_RTC_DRV_MACSMC)	+= rtc-macsmc.o
>  obj-$(CONFIG_RTC_DRV_MAX31335)	+= rtc-max31335.o
>  obj-$(CONFIG_RTC_DRV_MAX6900)	+= rtc-max6900.o
>  obj-$(CONFIG_RTC_DRV_MAX6902)	+= rtc-max6902.o
> diff --git a/drivers/rtc/rtc-macsmc.c b/drivers/rtc/rtc-macsmc.c
> new file mode 100644
> index 000000000000..05e360277f63
> --- /dev/null
> +++ b/drivers/rtc/rtc-macsmc.c
> @@ -0,0 +1,141 @@
> +// SPDX-License-Identifier: GPL-2.0-only OR MIT
> +/*
> + * Apple SMC RTC driver
> + * Copyright The Asahi Linux Contributors
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/mfd/core.h>

Why is this here?

> +#include <linux/mfd/macsmc.h>
> +#include <linux/module.h>
> +#include <linux/nvmem-consumer.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/rtc.h>
> +#include <linux/slab.h>

-- 
Lee Jones [李琼斯]