LXR linux/drivers/rtc/rtc-dm355evm.c

   1/*
   2 * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
   3 *
   4 * Copyright (c) 2008 by David Brownell
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11#include <linux/kernel.h>
  12#include <linux/init.h>
  13#include <linux/rtc.h>
  14#include <linux/platform_device.h>
  15
  16#include <linux/i2c/dm355evm_msp.h>
  17
  18
  19/*
  20 * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
  21 * a 1 Hz counter.  When a backup battery is supplied, that makes a
  22 * reasonable RTC for applications where alarms and non-NTP drift
  23 * compensation aren't important.
  24 *
  25 * The only real glitch is the inability to read or write all four
  26 * counter bytes atomically:  the count may increment in the middle
  27 * of an operation, causing trouble when the LSB rolls over.
  28 *
  29 * This driver was tested with firmware revision A4.
  30 */
  31union evm_time {
  32        u8      bytes[4];
  33        u32     value;
  34};
  35
  36static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
  37{
  38        union evm_time  time;
  39        int             status;
  40        int             tries = 0;
  41
  42        do {
  43                /*
  44                 * Read LSB(0) to MSB(3) bytes.  Defend against the counter
  45                 * rolling over by re-reading until the value is stable,
  46                 * and assuming the four reads take at most a few seconds.
  47                 */
  48                status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
  49                if (status < 0)
  50                        return status;
  51                if (tries && time.bytes[0] == status)
  52                        break;
  53                time.bytes[0] = status;
  54
  55                status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
  56                if (status < 0)
  57                        return status;
  58                if (tries && time.bytes[1] == status)
  59                        break;
  60                time.bytes[1] = status;
  61
  62                status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
  63                if (status < 0)
  64                        return status;
  65                if (tries && time.bytes[2] == status)
  66                        break;
  67                time.bytes[2] = status;
  68
  69                status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
  70                if (status < 0)
  71                        return status;
  72                if (tries && time.bytes[3] == status)
  73                        break;
  74                time.bytes[3] = status;
  75
  76        } while (++tries < 5);
  77
  78        dev_dbg(dev, "read timestamp %08x\n", time.value);
  79
  80        rtc_time_to_tm(le32_to_cpu(time.value), tm);
  81        return 0;
  82}
  83
  84static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
  85{
  86        union evm_time  time;
  87        unsigned long   value;
  88        int             status;
  89
  90        rtc_tm_to_time(tm, &value);
  91        time.value = cpu_to_le32(value);
  92
  93        dev_dbg(dev, "write timestamp %08x\n", time.value);
  94
  95        /*
  96         * REVISIT handle non-atomic writes ... maybe just retry until
  97         * byte[1] sticks (no rollover)?
  98         */
  99        status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
 100        if (status < 0)
 101                return status;
 102
 103        status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
 104        if (status < 0)
 105                return status;
 106
 107        status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
 108        if (status < 0)
 109                return status;
 110
 111        status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
 112        if (status < 0)
 113                return status;
 114
 115        return 0;
 116}
 117
 118static struct rtc_class_ops dm355evm_rtc_ops = {
 119        .read_time      = dm355evm_rtc_read_time,
 120        .set_time       = dm355evm_rtc_set_time,
 121};
 122
 123/*----------------------------------------------------------------------*/
 124
 125static int __devinit dm355evm_rtc_probe(struct platform_device *pdev)
 126{
 127        struct rtc_device *rtc;
 128
 129        rtc = rtc_device_register(pdev->name,
 130                                  &pdev->dev, &dm355evm_rtc_ops, THIS_MODULE);
 131        if (IS_ERR(rtc)) {
 132                dev_err(&pdev->dev, "can't register RTC device, err %ld\n",
 133                        PTR_ERR(rtc));
 134                return PTR_ERR(rtc);
 135        }
 136        platform_set_drvdata(pdev, rtc);
 137
 138        return 0;
 139}
 140
 141static int __devexit dm355evm_rtc_remove(struct platform_device *pdev)
 142{
 143        struct rtc_device *rtc = platform_get_drvdata(pdev);
 144
 145        rtc_device_unregister(rtc);
 146        platform_set_drvdata(pdev, NULL);
 147        return 0;
 148}
 149
 150/*
 151 * I2C is used to talk to the MSP430, but this platform device is
 152 * exposed by an MFD driver that manages I2C communications.
 153 */
 154static struct platform_driver rtc_dm355evm_driver = {
 155        .probe          = dm355evm_rtc_probe,
 156        .remove         = __devexit_p(dm355evm_rtc_remove),
 157        .driver         = {
 158                .owner  = THIS_MODULE,
 159                .name   = "rtc-dm355evm",
 160        },
 161};
 162
 163static int __init dm355evm_rtc_init(void)
 164{
 165        return platform_driver_register(&rtc_dm355evm_driver);
 166}
 167module_init(dm355evm_rtc_init);
 168
 169static void __exit dm355evm_rtc_exit(void)
 170{
 171        platform_driver_unregister(&rtc_dm355evm_driver);
 172}
 173module_exit(dm355evm_rtc_exit);
 174
 175MODULE_LICENSE("GPL");
 176