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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"); |