[PATCH v13 4/7] rtc: spacemit: support the SpacemiT P1 RTC

Alex Elder
2025-08-25T17:21:10Z

Add support for the RTC found in the SpacemiT P1 PMIC. Initially
only setting and reading the time are supported.

The PMIC is implemented as a multi-function device. This RTC is
probed based on this driver being named in a MFD cell in the simple
MFD I2C driver.

Signed-off-by: Alex Elder <elder@riscstar.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
---
drivers/rtc/Kconfig | 10 ++
drivers/rtc/Makefile | 1 +
drivers/rtc/rtc-spacemit-p1.c | 167 ++++++++++++++++++++++++++++++++++
3 files changed, 178 insertions(+)
create mode 100644 drivers/rtc/rtc-spacemit-p1.c

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 64f6e9756aff4..31d355b103d43 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -406,6 +406,16 @@ config RTC_DRV_MAX77686
This driver can also be built as a module. If so, the module
will be called rtc-max77686.

+config RTC_DRV_SPACEMIT_P1
+ tristate "SpacemiT P1 RTC"
+ depends on ARCH_SPACEMIT || COMPILE_TEST
+ select MFD_SPACEMIT_P1
+ default ARCH_SPACEMIT
+ help
+ Enable support for the RTC function in the SpacemiT P1 PMIC.
+ This driver can also be built as a module, which will be called
+ "spacemit-p1-rtc".
+
config RTC_DRV_NCT3018Y
tristate "Nuvoton NCT3018Y"
depends on OF
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 789bddfea99d8..f41fdb4fabae9 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -171,6 +171,7 @@ obj-$(CONFIG_RTC_DRV_SD2405AL) += rtc-sd2405al.o
obj-$(CONFIG_RTC_DRV_SD3078) += rtc-sd3078.o
obj-$(CONFIG_RTC_DRV_SH) += rtc-sh.o
obj-$(CONFIG_RTC_DRV_SNVS) += rtc-snvs.o
+obj-$(CONFIG_RTC_DRV_SPACEMIT_P1) += rtc-spacemit-p1.o
obj-$(CONFIG_RTC_DRV_SPEAR) += rtc-spear.o
obj-$(CONFIG_RTC_DRV_STARFIRE) += rtc-starfire.o
obj-$(CONFIG_RTC_DRV_STK17TA8) += rtc-stk17ta8.o
diff --git a/drivers/rtc/rtc-spacemit-p1.c b/drivers/rtc/rtc-spacemit-p1.c
new file mode 100644
index 0000000000000..43ab62494bb4b
--- /dev/null
+++ b/drivers/rtc/rtc-spacemit-p1.c
@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for the RTC found in the SpacemiT P1 PMIC
+ *
+ * Copyright (C) 2025 by RISCstar Solutions Corporation. All rights reserved.
+ */
+
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+
+#define MOD_NAME "spacemit-p1-rtc"
+
+/*
+ * Six consecutive 1-byte registers hold the seconds, minutes, hours,
+ * day-of-month, month, and year (respectively).
+ *
+ * The range of values in these registers is:
+ * seconds 0-59
+ * minutes 0-59
+ * hours 0-59
+ * day 0-30 (struct tm is 1-31)
+ * month 0-11
+ * year years since 2000 (struct tm is since 1900)
+ *
+ * Note that the day and month must be converted after reading and
+ * before writing.
+ */
+#define RTC_TIME 0x0d /* Offset of the seconds register */
+
+#define RTC_CTRL 0x1d
+#define RTC_EN BIT(2)
+
+/* Number of attempts to read a consistent time stamp before giving up */
+#define RTC_READ_TRIES 20 /* At least 1 */
+
+struct p1_rtc {
+ struct regmap *regmap;
+ struct rtc_device *rtc;
+};
+
+/*
+ * The P1 hardware documentation states that the register values are
+ * latched to ensure a consistent time snapshot within the registers,
+ * but these are in fact unstable due to a bug in the hardware design.
+ * So we loop until we get two identical readings.
+ */
+static int p1_rtc_read_time(struct device *dev, struct rtc_time *t)
+{
+ struct p1_rtc *p1 = dev_get_drvdata(dev);
+ struct regmap *regmap = p1->regmap;
+ u32 count = RTC_READ_TRIES;
+ u8 seconds;
+ u8 time[6];
+ int ret;
+
+ if (!regmap_test_bits(regmap, RTC_CTRL, RTC_EN))
+ return -EINVAL; /* RTC is disabled */
+
+ ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
+ if (ret)
+ return ret;
+
+ do {
+ seconds = time[0];
+ ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
+ if (ret)
+ return ret;
+ } while (time[0] != seconds && --count);
+
+ if (!count)
+ return -EIO; /* Unable to get a consistent result */
+
+ t->tm_sec = time[0] & GENMASK(5, 0);
+ t->tm_min = time[1] & GENMASK(5, 0);
+ t->tm_hour = time[2] & GENMASK(4, 0);
+ t->tm_mday = (time[3] & GENMASK(4, 0)) + 1;
+ t->tm_mon = time[4] & GENMASK(3, 0);
+ t->tm_year = (time[5] & GENMASK(5, 0)) + 100;
+
+ return 0;
+}
+
+/*
+ * The P1 hardware documentation states that values in the registers are
+ * latched so when written they represent a consistent time snapshot.
+ * Nevertheless, this is not guaranteed by the implementation, so we must
+ * disable the RTC while updating it.
+ */
+static int p1_rtc_set_time(struct device *dev, struct rtc_time *t)
+{
+ struct p1_rtc *p1 = dev_get_drvdata(dev);
+ struct regmap *regmap = p1->regmap;
+ u8 time[6];
+ int ret;
+
+ time[0] = t->tm_sec;
+ time[1] = t->tm_min;
+ time[2] = t->tm_hour;
+ time[3] = t->tm_mday - 1;
+ time[4] = t->tm_mon;
+ time[5] = t->tm_year - 100;
+
+ /* Disable the RTC to update; re-enable again when done */
+ ret = regmap_clear_bits(regmap, RTC_CTRL, RTC_EN);
+ if (ret)
+ return ret;
+
+ /* If something goes wrong, leave the RTC disabled */
+ ret = regmap_bulk_write(regmap, RTC_TIME, time, sizeof(time));
+ if (ret)
+ return ret;
+
+ return regmap_set_bits(regmap, RTC_CTRL, RTC_EN);
+}
+
+static const struct rtc_class_ops p1_rtc_class_ops = {
+ .read_time = p1_rtc_read_time,
+ .set_time = p1_rtc_set_time,
+};
+
+static int p1_rtc_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct rtc_device *rtc;
+ struct p1_rtc *p1;
+
+ p1 = devm_kzalloc(dev, sizeof(*p1), GFP_KERNEL);
+ if (!p1)
+ return -ENOMEM;
+ dev_set_drvdata(dev, p1);
+
+ p1->regmap = dev_get_regmap(dev->parent, NULL);
+ if (!p1->regmap)
+ return dev_err_probe(dev, -ENODEV, "failed to get regmap\n");
+
+ rtc = devm_rtc_allocate_device(dev);
+ if (IS_ERR(rtc))
+ return dev_err_probe(dev, PTR_ERR(rtc),
+ "error allocating device\n");
+ p1->rtc = rtc;
+
+ rtc->ops = &p1_rtc_class_ops;
+ rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+ rtc->range_max = RTC_TIMESTAMP_END_2063;
+
+ clear_bit(RTC_FEATURE_ALARM, rtc->features);
+ clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
+
+ return devm_rtc_register_device(rtc);
+}
+
+static struct platform_driver p1_rtc_driver = {
+ .probe = p1_rtc_probe,
+ .driver = {
+ .name = MOD_NAME,
+ },
+};
+
+module_platform_driver(p1_rtc_driver);
+
+MODULE_DESCRIPTION("SpacemiT P1 RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:" MOD_NAME);
--
2.48.1