rtc: Add new rtc-macsmc driver for Apple Silicon Macs

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@gompa.dev>
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Sven Peter <sven@kernel.org>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Link: https://patch.msgid.link/20251112-macsmc-subdevs-v5-3-728e4b91fe81@gmail.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/MAINTAINERS b/MAINTAINERS
index b93d26e60e995248c894d5b548c02e15c3769891..051abbe5953c5eb86e07b7df6452bfe653a71c25 100644 (file)
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2459,6 +2459,7 @@ 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 fc2154d6e413b87f4e9424ad9f2d041c09b4b4e8..9906cddd5a8b66b1649a59d8a4e748dc66cbf51f 100644 (file)
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -2098,6 +2098,17 @@ 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 e464a90be323e0d6b7fa436fe4ada54a6b65bbed..6cf7e066314e13c18c1ae0e284edbb16c1bd37e4 100644 (file)
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -94,6 +94,7 @@ 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 (file)
index 0000000..8fe8830
--- /dev/null
+++ b/drivers/rtc/rtc-macsmc.c
@@ -0,0 +1,140 @@
+// 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/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>
+
+/* 48-bit RTC */
+#define RTC_BYTES 6
+#define RTC_BITS (8 * RTC_BYTES)
+
+/* 32768 Hz clock */
+#define RTC_SEC_SHIFT 15
+
+struct macsmc_rtc {
+       struct device *dev;
+       struct apple_smc *smc;
+       struct rtc_device *rtc_dev;
+       struct nvmem_cell *rtc_offset;
+};
+
+static int macsmc_rtc_get_time(struct device *dev, struct rtc_time *tm)
+{
+       struct macsmc_rtc *rtc = dev_get_drvdata(dev);
+       u64 ctr = 0, off = 0;
+       time64_t now;
+       void *p_off;
+       size_t len;
+       int ret;
+
+       ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES);
+       if (ret < 0)
+               return ret;
+       if (ret != RTC_BYTES)
+               return -EIO;
+
+       p_off = nvmem_cell_read(rtc->rtc_offset, &len);
+       if (IS_ERR(p_off))
+               return PTR_ERR(p_off);
+       if (len < RTC_BYTES) {
+               kfree(p_off);
+               return -EIO;
+       }
+
+       memcpy(&off, p_off, RTC_BYTES);
+       kfree(p_off);
+
+       /* Sign extend from 48 to 64 bits, then arithmetic shift right 15 bits to get seconds */
+       now = sign_extend64(ctr + off, RTC_BITS - 1) >> RTC_SEC_SHIFT;
+       rtc_time64_to_tm(now, tm);
+
+       return ret;
+}
+
+static int macsmc_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+       struct macsmc_rtc *rtc = dev_get_drvdata(dev);
+       u64 ctr = 0, off = 0;
+       int ret;
+
+       ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES);
+       if (ret < 0)
+               return ret;
+       if (ret != RTC_BYTES)
+               return -EIO;
+
+       /* This sets the offset such that the set second begins now */
+       off = (rtc_tm_to_time64(tm) << RTC_SEC_SHIFT) - ctr;
+       return nvmem_cell_write(rtc->rtc_offset, &off, RTC_BYTES);
+}
+
+static const struct rtc_class_ops macsmc_rtc_ops = {
+       .read_time = macsmc_rtc_get_time,
+       .set_time = macsmc_rtc_set_time,
+};
+
+static int macsmc_rtc_probe(struct platform_device *pdev)
+{
+       struct apple_smc *smc = dev_get_drvdata(pdev->dev.parent);
+       struct macsmc_rtc *rtc;
+
+       /*
+        * MFD will probe this device even without a node in the device tree,
+        * thus bail out early if the SMC on the current machines does not
+        * support RTC and has no node in the device tree.
+        */
+       if (!pdev->dev.of_node)
+               return -ENODEV;
+
+       rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+       if (!rtc)
+               return -ENOMEM;
+
+       rtc->dev = &pdev->dev;
+       rtc->smc = smc;
+
+       rtc->rtc_offset = devm_nvmem_cell_get(&pdev->dev, "rtc_offset");
+       if (IS_ERR(rtc->rtc_offset))
+               return dev_err_probe(&pdev->dev, PTR_ERR(rtc->rtc_offset),
+                                    "Failed to get rtc_offset NVMEM cell\n");
+
+       rtc->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+       if (IS_ERR(rtc->rtc_dev))
+               return PTR_ERR(rtc->rtc_dev);
+
+       rtc->rtc_dev->ops = &macsmc_rtc_ops;
+       rtc->rtc_dev->range_min = S64_MIN >> (RTC_SEC_SHIFT + (64 - RTC_BITS));
+       rtc->rtc_dev->range_max = S64_MAX >> (RTC_SEC_SHIFT + (64 - RTC_BITS));
+
+       platform_set_drvdata(pdev, rtc);
+
+       return devm_rtc_register_device(rtc->rtc_dev);
+}
+
+static const struct of_device_id macsmc_rtc_of_table[] = {
+       { .compatible = "apple,smc-rtc", },
+       {}
+};
+MODULE_DEVICE_TABLE(of, macsmc_rtc_of_table);
+
+static struct platform_driver macsmc_rtc_driver = {
+       .driver = {
+               .name = "macsmc-rtc",
+               .of_match_table = macsmc_rtc_of_table,
+       },
+       .probe = macsmc_rtc_probe,
+};
+module_platform_driver(macsmc_rtc_driver);
+
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_DESCRIPTION("Apple SMC RTC driver");
+MODULE_AUTHOR("Hector Martin <marcan@marcan.st>");