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
dm355evm_rtc_read_time(struct device * dev,struct rtc_time * tm)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
dm355evm_rtc_set_time(struct device * dev,struct rtc_time * tm)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
dm355evm_rtc_probe(struct platform_device * pdev)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
dm355evm_rtc_remove(struct platform_device * pdev)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
dm355evm_rtc_init(void)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
dm355evm_rtc_exit(void)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");
176