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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> | |
2113852b | 17 | #include <linux/module.h> |
afd8d0f9 DB |
18 | |
19 | ||
20 | /* | |
21 | * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed | |
22 | * a 1 Hz counter. When a backup battery is supplied, that makes a | |
23 | * reasonable RTC for applications where alarms and non-NTP drift | |
24 | * compensation aren't important. | |
25 | * | |
26 | * The only real glitch is the inability to read or write all four | |
27 | * counter bytes atomically: the count may increment in the middle | |
28 | * of an operation, causing trouble when the LSB rolls over. | |
29 | * | |
30 | * This driver was tested with firmware revision A4. | |
31 | */ | |
32 | union evm_time { | |
33 | u8 bytes[4]; | |
34 | u32 value; | |
35 | }; | |
36 | ||
37 | static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm) | |
38 | { | |
39 | union evm_time time; | |
40 | int status; | |
41 | int tries = 0; | |
42 | ||
43 | do { | |
44 | /* | |
45 | * Read LSB(0) to MSB(3) bytes. Defend against the counter | |
46 | * rolling over by re-reading until the value is stable, | |
47 | * and assuming the four reads take at most a few seconds. | |
48 | */ | |
49 | status = dm355evm_msp_read(DM355EVM_MSP_RTC_0); | |
50 | if (status < 0) | |
51 | return status; | |
52 | if (tries && time.bytes[0] == status) | |
53 | break; | |
54 | time.bytes[0] = status; | |
55 | ||
56 | status = dm355evm_msp_read(DM355EVM_MSP_RTC_1); | |
57 | if (status < 0) | |
58 | return status; | |
59 | if (tries && time.bytes[1] == status) | |
60 | break; | |
61 | time.bytes[1] = status; | |
62 | ||
63 | status = dm355evm_msp_read(DM355EVM_MSP_RTC_2); | |
64 | if (status < 0) | |
65 | return status; | |
66 | if (tries && time.bytes[2] == status) | |
67 | break; | |
68 | time.bytes[2] = status; | |
69 | ||
70 | status = dm355evm_msp_read(DM355EVM_MSP_RTC_3); | |
71 | if (status < 0) | |
72 | return status; | |
73 | if (tries && time.bytes[3] == status) | |
74 | break; | |
75 | time.bytes[3] = status; | |
76 | ||
77 | } while (++tries < 5); | |
78 | ||
79 | dev_dbg(dev, "read timestamp %08x\n", time.value); | |
80 | ||
81 | rtc_time_to_tm(le32_to_cpu(time.value), tm); | |
82 | return 0; | |
83 | } | |
84 | ||
85 | static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm) | |
86 | { | |
87 | union evm_time time; | |
88 | unsigned long value; | |
89 | int status; | |
90 | ||
91 | rtc_tm_to_time(tm, &value); | |
92 | time.value = cpu_to_le32(value); | |
93 | ||
94 | dev_dbg(dev, "write timestamp %08x\n", time.value); | |
95 | ||
96 | /* | |
97 | * REVISIT handle non-atomic writes ... maybe just retry until | |
98 | * byte[1] sticks (no rollover)? | |
99 | */ | |
100 | status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0); | |
101 | if (status < 0) | |
102 | return status; | |
103 | ||
104 | status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1); | |
105 | if (status < 0) | |
106 | return status; | |
107 | ||
108 | status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2); | |
109 | if (status < 0) | |
110 | return status; | |
111 | ||
112 | status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3); | |
113 | if (status < 0) | |
114 | return status; | |
115 | ||
116 | return 0; | |
117 | } | |
118 | ||
119 | static struct rtc_class_ops dm355evm_rtc_ops = { | |
120 | .read_time = dm355evm_rtc_read_time, | |
121 | .set_time = dm355evm_rtc_set_time, | |
122 | }; | |
123 | ||
124 | /*----------------------------------------------------------------------*/ | |
125 | ||
126 | static int __devinit dm355evm_rtc_probe(struct platform_device *pdev) | |
127 | { | |
128 | struct rtc_device *rtc; | |
129 | ||
130 | rtc = rtc_device_register(pdev->name, | |
131 | &pdev->dev, &dm355evm_rtc_ops, THIS_MODULE); | |
132 | if (IS_ERR(rtc)) { | |
133 | dev_err(&pdev->dev, "can't register RTC device, err %ld\n", | |
134 | PTR_ERR(rtc)); | |
135 | return PTR_ERR(rtc); | |
136 | } | |
137 | platform_set_drvdata(pdev, rtc); | |
138 | ||
139 | return 0; | |
140 | } | |
141 | ||
142 | static int __devexit dm355evm_rtc_remove(struct platform_device *pdev) | |
143 | { | |
144 | struct rtc_device *rtc = platform_get_drvdata(pdev); | |
145 | ||
146 | rtc_device_unregister(rtc); | |
147 | platform_set_drvdata(pdev, NULL); | |
148 | return 0; | |
149 | } | |
150 | ||
151 | /* | |
152 | * I2C is used to talk to the MSP430, but this platform device is | |
153 | * exposed by an MFD driver that manages I2C communications. | |
154 | */ | |
155 | static struct platform_driver rtc_dm355evm_driver = { | |
156 | .probe = dm355evm_rtc_probe, | |
157 | .remove = __devexit_p(dm355evm_rtc_remove), | |
158 | .driver = { | |
159 | .owner = THIS_MODULE, | |
160 | .name = "rtc-dm355evm", | |
161 | }, | |
162 | }; | |
163 | ||
164 | static int __init dm355evm_rtc_init(void) | |
165 | { | |
166 | return platform_driver_register(&rtc_dm355evm_driver); | |
167 | } | |
168 | module_init(dm355evm_rtc_init); | |
169 | ||
170 | static void __exit dm355evm_rtc_exit(void) | |
171 | { | |
172 | platform_driver_unregister(&rtc_dm355evm_driver); | |
173 | } | |
174 | module_exit(dm355evm_rtc_exit); | |
175 | ||
176 | MODULE_LICENSE("GPL"); |