1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * arch/sh/boards/dreamcast/rtc.c
4  *
5  * Dreamcast AICA RTC routines.
6  *
7  * Copyright (c) 2001, 2002 M. R. Brown <mrbrown@0xd6.org>
8  * Copyright (c) 2002 Paul Mundt <lethal@chaoticdreams.org>
9  */
10 
11 #include <linux/time.h>
12 #include <linux/rtc.h>
13 #include <linux/io.h>
14 #include <linux/platform_device.h>
15 
16 /* The AICA RTC has an Epoch of 1/1/1950, so we must subtract 20 years (in
17    seconds) to get the standard Unix Epoch when getting the time, and add
18    20 years when setting the time. */
19 #define TWENTY_YEARS ((20 * 365LU + 5) * 86400)
20 
21 /* The AICA RTC is represented by a 32-bit seconds counter stored in 2 16-bit
22    registers.*/
23 #define AICA_RTC_SECS_H		0xa0710000
24 #define AICA_RTC_SECS_L		0xa0710004
25 
26 /**
27  * aica_rtc_gettimeofday - Get the time from the AICA RTC
28  * @dev: the RTC device (ignored)
29  * @tm: pointer to resulting RTC time structure
30  *
31  * Grabs the current RTC seconds counter and adjusts it to the Unix Epoch.
32  */
33 static int aica_rtc_gettimeofday(struct device *dev, struct rtc_time *tm)
34 {
35 	unsigned long val1, val2;
36 	time64_t t;
37 
38 	do {
39 		val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
40 			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
41 
42 		val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
43 			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
44 	} while (val1 != val2);
45 
46 	/* normalize to 1970..2106 time range */
47 	t = (u32)(val1 - TWENTY_YEARS);
48 
49 	rtc_time64_to_tm(t, tm);
50 
51 	return 0;
52 }
53 
54 /**
55  * aica_rtc_settimeofday - Set the AICA RTC to the current time
56  * @dev: the RTC device (ignored)
57  * @tm: pointer to new RTC time structure
58  *
59  * Adjusts the given @tv to the AICA Epoch and sets the RTC seconds counter.
60  */
61 static int aica_rtc_settimeofday(struct device *dev, struct rtc_time *tm)
62 {
63 	unsigned long val1, val2;
64 	time64_t secs = rtc_tm_to_time64(tm);
65 	u32 adj = secs + TWENTY_YEARS;
66 
67 	do {
68 		__raw_writel((adj & 0xffff0000) >> 16, AICA_RTC_SECS_H);
69 		__raw_writel((adj & 0xffff), AICA_RTC_SECS_L);
70 
71 		val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
72 			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
73 
74 		val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
75 			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
76 	} while (val1 != val2);
77 
78 	return 0;
79 }
80 
81 static const struct rtc_class_ops rtc_generic_ops = {
82 	.read_time = aica_rtc_gettimeofday,
83 	.set_time = aica_rtc_settimeofday,
84 };
85 
86 static int __init aica_time_init(void)
87 {
88 	struct platform_device *pdev;
89 
90 	pdev = platform_device_register_data(NULL, "rtc-generic", -1,
91 					     &rtc_generic_ops,
92 					     sizeof(rtc_generic_ops));
93 
94 	return PTR_ERR_OR_ZERO(pdev);
95 }
96 arch_initcall(aica_time_init);
97