[PATCH v9 5/7] rtc: New driver for RTC in Netronix embedded controller

Jonathan Neuschäfer
2021-01-24T22:46:18Z

With this driver, mainline Linux can keep its time and date in sync with
the vendor kernel.

Advanced functionality like alarm and automatic power-on is not yet
supported.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
---
v9:
- no changes

v8:
- https://lore.kernel.org/lkml/20210116194826.3866540-6-j.neuschaefer@gmx.net/
- Copy dev.of_node from parent device

v7:
- Adjust to recent RTC API change (rtc_register_device -> devm_rtc_register_device)

v6:
- no changes

v5:
- Add Alexandre Belloni's A-b
- Use regmap_multi_reg_write

v4:
- Remove "driver" from Kconfig entry for consistency with most other entries
- Add missing MODULE_ALIAS line
- Give NTXEC_REG_READ_ macros longer names
- Solve the read tearing issue using Alexandre Belloni's algorithm
- Solve the write tearing issue using Uwe Kleine-König's algorithm
- Spell out ODM

v3:
- Add email address to copyright line
- Remove OF compatible string and don't include linux/of_device.h
- Don't use a comma after sentinels
- Avoid ret |= ... pattern
- Move 8-bit register conversion to ntxec.h
- Relicense as GPLv2 or later

v2:
- Rework top-of-file comment [Lee Jones]
- Sort the #include lines [Alexandre Belloni]
- don't align = signs in struct initializers [Uwe Kleine-König]
- Switch to regmap
- Fix register number used to read minutes and seconds
- Prefix registers with NTXEC_REG_
- Add help text to the Kconfig option
- Use devm_rtc_allocate_device and rtc_register_device, set ->range_min and ->range_max
---
drivers/rtc/Kconfig | 8 +++
drivers/rtc/Makefile | 1 +
drivers/rtc/rtc-ntxec.c | 145 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 154 insertions(+)
create mode 100644 drivers/rtc/rtc-ntxec.c

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 6123f9f4fbc90..d49cf387add14 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -1315,6 +1315,14 @@ config RTC_DRV_CROS_EC
This driver can also be built as a module. If so, the module
will be called rtc-cros-ec.

+config RTC_DRV_NTXEC
+ tristate "Netronix embedded controller RTC"
+ depends on MFD_NTXEC
+ help
+ Say yes here if you want to support the RTC functionality of the
+ embedded controller found in certain e-book readers designed by the
+ original design manufacturer Netronix.
+
comment "on-CPU RTC drivers"

config RTC_DRV_ASM9260
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index bb8f319b09fbf..92c26eafe70ce 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -110,6 +110,7 @@ obj-$(CONFIG_RTC_DRV_MT7622) += rtc-mt7622.o
obj-$(CONFIG_RTC_DRV_MV) += rtc-mv.o
obj-$(CONFIG_RTC_DRV_MXC) += rtc-mxc.o
obj-$(CONFIG_RTC_DRV_MXC_V2) += rtc-mxc_v2.o
+obj-$(CONFIG_RTC_DRV_NTXEC) += rtc-ntxec.o
obj-$(CONFIG_RTC_DRV_OMAP) += rtc-omap.o
obj-$(CONFIG_RTC_DRV_OPAL) += rtc-opal.o
obj-$(CONFIG_RTC_DRV_PALMAS) += rtc-palmas.o
diff --git a/drivers/rtc/rtc-ntxec.c b/drivers/rtc/rtc-ntxec.c
new file mode 100644
index 0000000000000..850ca49186fdc
--- /dev/null
+++ b/drivers/rtc/rtc-ntxec.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * The Netronix embedded controller is a microcontroller found in some
+ * e-book readers designed by the original design manufacturer Netronix, Inc.
+ * It contains RTC, battery monitoring, system power management, and PWM
+ * functionality.
+ *
+ * This driver implements access to the RTC time and date.
+ *
+ * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>
+ */
+
+#include <linux/mfd/ntxec.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+#include <linux/types.h>
+
+struct ntxec_rtc {
+ struct device *dev;
+ struct ntxec *ec;
+};
+
+#define NTXEC_REG_WRITE_YEAR 0x10
+#define NTXEC_REG_WRITE_MONTH 0x11
+#define NTXEC_REG_WRITE_DAY 0x12
+#define NTXEC_REG_WRITE_HOUR 0x13
+#define NTXEC_REG_WRITE_MINUTE 0x14
+#define NTXEC_REG_WRITE_SECOND 0x15
+
+#define NTXEC_REG_READ_YEAR_MONTH 0x20
+#define NTXEC_REG_READ_MDAY_HOUR 0x21
+#define NTXEC_REG_READ_MINUTE_SECOND 0x23
+
+static int ntxec_read_time(struct device *dev, struct rtc_time *tm)
+{
+ struct ntxec_rtc *rtc = dev_get_drvdata(dev);
+ unsigned int value;
+ int res;
+
+retry:
+ res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MINUTE_SECOND, &value);
+ if (res < 0)
+ return res;
+
+ tm->tm_min = value >> 8;
+ tm->tm_sec = value & 0xff;
+
+ res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MDAY_HOUR, &value);
+ if (res < 0)
+ return res;
+
+ tm->tm_mday = value >> 8;
+ tm->tm_hour = value & 0xff;
+
+ res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_YEAR_MONTH, &value);
+ if (res < 0)
+ return res;
+
+ tm->tm_year = (value >> 8) + 100;
+ tm->tm_mon = (value & 0xff) - 1;
+
+ /*
+ * Read the minutes/seconds field again. If it changed since the first
+ * read, we can't assume that the values read so far are consistent,
+ * and should start from the beginning.
+ */
+ res = regmap_read(rtc->ec->regmap, NTXEC_REG_READ_MINUTE_SECOND, &value);
+ if (res < 0)
+ return res;
+
+ if (tm->tm_min != value >> 8 || tm->tm_sec != (value & 0xff))
+ goto retry;
+
+ return 0;
+}
+
+static int ntxec_set_time(struct device *dev, struct rtc_time *tm)
+{
+ struct ntxec_rtc *rtc = dev_get_drvdata(dev);
+
+ /*
+ * To avoid time overflows while we're writing the full date/time,
+ * set the seconds field to zero before doing anything else. For the
+ * next 59 seconds (plus however long it takes until the RTC's next
+ * update of the second field), the seconds field will not overflow
+ * into the other fields.
+ */
+ struct reg_sequence regs[] = {
+ { NTXEC_REG_WRITE_SECOND, ntxec_reg8(0) },
+ { NTXEC_REG_WRITE_YEAR, ntxec_reg8(tm->tm_year - 100) },
+ { NTXEC_REG_WRITE_MONTH, ntxec_reg8(tm->tm_mon + 1) },
+ { NTXEC_REG_WRITE_DAY, ntxec_reg8(tm->tm_mday) },
+ { NTXEC_REG_WRITE_HOUR, ntxec_reg8(tm->tm_hour) },
+ { NTXEC_REG_WRITE_MINUTE, ntxec_reg8(tm->tm_min) },
+ { NTXEC_REG_WRITE_SECOND, ntxec_reg8(tm->tm_sec) },
+ };
+
+ return regmap_multi_reg_write(rtc->ec->regmap, regs, ARRAY_SIZE(regs));
+}
+
+static const struct rtc_class_ops ntxec_rtc_ops = {
+ .read_time = ntxec_read_time,
+ .set_time = ntxec_set_time,
+};
+
+static int ntxec_rtc_probe(struct platform_device *pdev)
+{
+ struct rtc_device *dev;
+ struct ntxec_rtc *rtc;
+
+ pdev->dev.of_node = pdev->dev.parent->of_node;
+
+ rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+ if (!rtc)
+ return -ENOMEM;
+
+ rtc->dev = &pdev->dev;
+ rtc->ec = dev_get_drvdata(pdev->dev.parent);
+ platform_set_drvdata(pdev, rtc);
+
+ dev = devm_rtc_allocate_device(&pdev->dev);
+ if (IS_ERR(dev))
+ return PTR_ERR(dev);
+
+ dev->ops = &ntxec_rtc_ops;
+ dev->range_min = RTC_TIMESTAMP_BEGIN_2000;
+ dev->range_max = 9025257599LL; /* 2255-12-31 23:59:59 */
+
+ return devm_rtc_register_device(dev);
+}
+
+static struct platform_driver ntxec_rtc_driver = {
+ .driver = {
+ .name = "ntxec-rtc",
+ },
+ .probe = ntxec_rtc_probe,
+};
+module_platform_driver(ntxec_rtc_driver);
+
+MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");
+MODULE_DESCRIPTION("RTC driver for Netronix EC");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ntxec-rtc");
--
2.29.2