--- /dev/null
+/*
+ * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
+ *
+ * Copyright (c) 2008 by David Brownell
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+
+#include <linux/i2c/dm355evm_msp.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_time_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;
+
+ rtc_tm_to_time(tm, &value);
+ 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 struct rtc_class_ops dm355evm_rtc_ops = {
+ .read_time = dm355evm_rtc_read_time,
+ .set_time = dm355evm_rtc_set_time,
+};
+
+/*----------------------------------------------------------------------*/
+
+static int __devinit dm355evm_rtc_probe(struct platform_device *pdev)
+{
+ struct rtc_device *rtc;
+
+ rtc = rtc_device_register(pdev->name,
+ &pdev->dev, &dm355evm_rtc_ops, THIS_MODULE);
+ if (IS_ERR(rtc)) {
+ dev_err(&pdev->dev, "can't register RTC device, err %ld\n",
+ PTR_ERR(rtc));
+ return PTR_ERR(rtc);
+ }
+ platform_set_drvdata(pdev, rtc);
+
+ return 0;
+}
+
+static int __devexit dm355evm_rtc_remove(struct platform_device *pdev)
+{
+ struct rtc_device *rtc = platform_get_drvdata(pdev);
+
+ rtc_device_unregister(rtc);
+ platform_set_drvdata(pdev, NULL);
+ return 0;
+}
+
+/*
+ * 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,
+ .remove = __devexit_p(dm355evm_rtc_remove),
+ .driver = {
+ .owner = THIS_MODULE,
+ .name = "rtc-dm355evm",
+ },
+};
+
+static int __init dm355evm_rtc_init(void)
+{
+ return platform_driver_register(&rtc_dm355evm_driver);
+}
+module_init(dm355evm_rtc_init);
+
+static void __exit dm355evm_rtc_exit(void)
+{
+ platform_driver_unregister(&rtc_dm355evm_driver);
+}
+module_exit(dm355evm_rtc_exit);
+
+MODULE_LICENSE("GPL");
projects / platform / kernel / kernel-mfld-blackbay.git / commitdiff