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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
4 *
5 * Copyright (c) 2008 by David Brownell
6 */
7#include <linux/kernel.h>
8#include <linux/init.h>
9#include <linux/rtc.h>
10#include <linux/platform_device.h>
11
12#include <linux/mfd/dm355evm_msp.h>
13#include <linux/module.h>
14
15
16/*
17 * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
18 * a 1 Hz counter. When a backup battery is supplied, that makes a
19 * reasonable RTC for applications where alarms and non-NTP drift
20 * compensation aren't important.
21 *
22 * The only real glitch is the inability to read or write all four
23 * counter bytes atomically: the count may increment in the middle
24 * of an operation, causing trouble when the LSB rolls over.
25 *
26 * This driver was tested with firmware revision A4.
27 */
28union evm_time {
29 u8 bytes[4];
30 u32 value;
31};
32
33static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
34{
35 union evm_time time;
36 int status;
37 int tries = 0;
38
39 do {
40 /*
41 * Read LSB(0) to MSB(3) bytes. Defend against the counter
42 * rolling over by re-reading until the value is stable,
43 * and assuming the four reads take at most a few seconds.
44 */
45 status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
46 if (status < 0)
47 return status;
48 if (tries && time.bytes[0] == status)
49 break;
50 time.bytes[0] = status;
51
52 status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
53 if (status < 0)
54 return status;
55 if (tries && time.bytes[1] == status)
56 break;
57 time.bytes[1] = status;
58
59 status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
60 if (status < 0)
61 return status;
62 if (tries && time.bytes[2] == status)
63 break;
64 time.bytes[2] = status;
65
66 status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
67 if (status < 0)
68 return status;
69 if (tries && time.bytes[3] == status)
70 break;
71 time.bytes[3] = status;
72
73 } while (++tries < 5);
74
75 dev_dbg(dev, "read timestamp %08x\n", time.value);
76
77 rtc_time64_to_tm(le32_to_cpu(time.value), tm);
78 return 0;
79}
80
81static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
82{
83 union evm_time time;
84 unsigned long value;
85 int status;
86
87 value = rtc_tm_to_time64(tm);
88 time.value = cpu_to_le32(value);
89
90 dev_dbg(dev, "write timestamp %08x\n", time.value);
91
92 /*
93 * REVISIT handle non-atomic writes ... maybe just retry until
94 * byte[1] sticks (no rollover)?
95 */
96 status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
97 if (status < 0)
98 return status;
99
100 status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
101 if (status < 0)
102 return status;
103
104 status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
105 if (status < 0)
106 return status;
107
108 status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
109 if (status < 0)
110 return status;
111
112 return 0;
113}
114
115static const struct rtc_class_ops dm355evm_rtc_ops = {
116 .read_time = dm355evm_rtc_read_time,
117 .set_time = dm355evm_rtc_set_time,
118};
119
120/*----------------------------------------------------------------------*/
121
122static int dm355evm_rtc_probe(struct platform_device *pdev)
123{
124 struct rtc_device *rtc;
125
126 rtc = devm_rtc_allocate_device(&pdev->dev);
127 if (IS_ERR(rtc))
128 return PTR_ERR(rtc);
129
130 platform_set_drvdata(pdev, rtc);
131
132 rtc->ops = &dm355evm_rtc_ops;
133 rtc->range_max = U32_MAX;
134
135 return rtc_register_device(rtc);
136}
137
138/*
139 * I2C is used to talk to the MSP430, but this platform device is
140 * exposed by an MFD driver that manages I2C communications.
141 */
142static struct platform_driver rtc_dm355evm_driver = {
143 .probe = dm355evm_rtc_probe,
144 .driver = {
145 .name = "rtc-dm355evm",
146 },
147};
148
149module_platform_driver(rtc_dm355evm_driver);
150
151MODULE_LICENSE("GPL");
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/mfd/dm355evm_msp.h>
17#include <linux/module.h>
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 */
32union evm_time {
33 u8 bytes[4];
34 u32 value;
35};
36
37static 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
85static 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
119static const 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
126static int dm355evm_rtc_probe(struct platform_device *pdev)
127{
128 struct rtc_device *rtc;
129
130 rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
131 &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/*
143 * I2C is used to talk to the MSP430, but this platform device is
144 * exposed by an MFD driver that manages I2C communications.
145 */
146static struct platform_driver rtc_dm355evm_driver = {
147 .probe = dm355evm_rtc_probe,
148 .driver = {
149 .name = "rtc-dm355evm",
150 },
151};
152
153module_platform_driver(rtc_dm355evm_driver);
154
155MODULE_LICENSE("GPL");