1 files changed, 151 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-dm355evm.c b/drivers/rtc/rtc-dm355evm.c
new file mode 100644
index 000000000..cd947a208
--- /dev/null
+++ b/drivers/rtc/rtc-dm355evm.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
+ *
+ * Copyright (c) 2008 by David Brownell
+ */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+
+#include <linux/mfd/dm355evm_msp.h>
+#include <linux/module.h>
+
+
+/*
+ * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
+ * a 1 Hz counter.  When a backup battery is supplied, that makes a
+ * reasonable RTC for applications where alarms and non-NTP drift
+ * compensation aren't important.
+ *
+ * The only real glitch is the inability to read or write all four
+ * counter bytes atomically:  the count may increment in the middle
+ * of an operation, causing trouble when the LSB rolls over.
+ *
+ * This driver was tested with firmware revision A4.
+ */
+union evm_time {
+	u8	bytes[4];
+	u32	value;
+};
+
+static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	union evm_time	time;
+	int		status;
+	int		tries = 0;
+
+	do {
+		/*
+		 * Read LSB(0) to MSB(3) bytes.  Defend against the counter
+		 * rolling over by re-reading until the value is stable,
+		 * and assuming the four reads take at most a few seconds.
+		 */
+		status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
+		if (status < 0)
+			return status;
+		if (tries && time.bytes[0] == status)
+			break;
+		time.bytes[0] = status;
+
+		status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
+		if (status < 0)
+			return status;
+		if (tries && time.bytes[1] == status)
+			break;
+		time.bytes[1] = status;
+
+		status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
+		if (status < 0)
+			return status;
+		if (tries && time.bytes[2] == status)
+			break;
+		time.bytes[2] = status;
+
+		status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
+		if (status < 0)
+			return status;
+		if (tries && time.bytes[3] == status)
+			break;
+		time.bytes[3] = status;
+
+	} while (++tries < 5);
+
+	dev_dbg(dev, "read timestamp %08x\n", time.value);
+
+	rtc_time64_to_tm(le32_to_cpu(time.value), tm);
+	return 0;
+}
+
+static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	union evm_time	time;
+	unsigned long	value;
+	int		status;
+
+	value = rtc_tm_to_time64(tm);
+	time.value = cpu_to_le32(value);
+
+	dev_dbg(dev, "write timestamp %08x\n", time.value);
+
+	/*
+	 * REVISIT handle non-atomic writes ... maybe just retry until
+	 * byte[1] sticks (no rollover)?
+	 */
+	status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
+	if (status < 0)
+		return status;
+
+	status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
+	if (status < 0)
+		return status;
+
+	status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
+	if (status < 0)
+		return status;
+
+	status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
+	if (status < 0)
+		return status;
+
+	return 0;
+}
+
+static const struct rtc_class_ops dm355evm_rtc_ops = {
+	.read_time	= dm355evm_rtc_read_time,
+	.set_time	= dm355evm_rtc_set_time,
+};
+
+/*----------------------------------------------------------------------*/
+
+static int dm355evm_rtc_probe(struct platform_device *pdev)
+{
+	struct rtc_device *rtc;
+
+	rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	platform_set_drvdata(pdev, rtc);
+
+	rtc->ops = &dm355evm_rtc_ops;
+	rtc->range_max = U32_MAX;
+
+	return rtc_register_device(rtc);
+}
+
+/*
+ * I2C is used to talk to the MSP430, but this platform device is
+ * exposed by an MFD driver that manages I2C communications.
+ */
+static struct platform_driver rtc_dm355evm_driver = {
+	.probe		= dm355evm_rtc_probe,
+	.driver		= {
+		.name	= "rtc-dm355evm",
+	},
+};
+
+module_platform_driver(rtc_dm355evm_driver);
+
+MODULE_LICENSE("GPL");