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  */
  31 union evm_time {
  32         u8      bytes[4];
  33         u32     value;
  34 };
  35
  36 static 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
  84 static 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
 118 static 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
 125 static 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
 141 static 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  */
 154 static 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
 163 static int __init dm355evm_rtc_init(void)
 164 {
 165         return platform_driver_register(&rtc_dm355evm_driver);
 166 }
 167 module_init(dm355evm_rtc_init);
 168
 169 static void __exit dm355evm_rtc_exit(void)
 170 {
 171         platform_driver_unregister(&rtc_dm355evm_driver);
 172 }
 173 module_exit(dm355evm_rtc_exit);
 174
 175 MODULE_LICENSE("GPL");