Loading...
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 | /*
* 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>
#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_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",
},
};
module_platform_driver(rtc_dm355evm_driver);
MODULE_LICENSE("GPL");
|