brd: limit 'max_part' module param to DISK_MAX_PARTS
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / drivers / rtc / rtc-dm355evm.c
blob58d4e18530da1ca4020c1046709b7d8cdadc639c
1 /*
2 * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
4 * Copyright (c) 2008 by David Brownell
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.
11 #include <linux/kernel.h>
12 #include <linux/init.h>
13 #include <linux/rtc.h>
14 #include <linux/platform_device.h>
16 #include <linux/i2c/dm355evm_msp.h>
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.
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.
29 * This driver was tested with firmware revision A4.
31 union evm_time {
32 u8 bytes[4];
33 u32 value;
36 static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
38 union evm_time time;
39 int status;
40 int tries = 0;
42 do {
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.
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;
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;
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;
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;
76 } while (++tries < 5);
78 dev_dbg(dev, "read timestamp %08x\n", time.value);
80 rtc_time_to_tm(le32_to_cpu(time.value), tm);
81 return 0;
84 static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
86 union evm_time time;
87 unsigned long value;
88 int status;
90 rtc_tm_to_time(tm, &value);
91 time.value = cpu_to_le32(value);
93 dev_dbg(dev, "write timestamp %08x\n", time.value);
96 * REVISIT handle non-atomic writes ... maybe just retry until
97 * byte[1] sticks (no rollover)?
99 status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
100 if (status < 0)
101 return status;
103 status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
104 if (status < 0)
105 return status;
107 status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
108 if (status < 0)
109 return status;
111 status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
112 if (status < 0)
113 return status;
115 return 0;
118 static struct rtc_class_ops dm355evm_rtc_ops = {
119 .read_time = dm355evm_rtc_read_time,
120 .set_time = dm355evm_rtc_set_time,
123 /*----------------------------------------------------------------------*/
125 static int __devinit dm355evm_rtc_probe(struct platform_device *pdev)
127 struct rtc_device *rtc;
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);
136 platform_set_drvdata(pdev, rtc);
138 return 0;
141 static int __devexit dm355evm_rtc_remove(struct platform_device *pdev)
143 struct rtc_device *rtc = platform_get_drvdata(pdev);
145 rtc_device_unregister(rtc);
146 platform_set_drvdata(pdev, NULL);
147 return 0;
151 * I2C is used to talk to the MSP430, but this platform device is
152 * exposed by an MFD driver that manages I2C communications.
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",
163 static int __init dm355evm_rtc_init(void)
165 return platform_driver_register(&rtc_dm355evm_driver);
167 module_init(dm355evm_rtc_init);
169 static void __exit dm355evm_rtc_exit(void)
171 platform_driver_unregister(&rtc_dm355evm_driver);
173 module_exit(dm355evm_rtc_exit);
175 MODULE_LICENSE("GPL");