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 */
33static 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 */
61static 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
81static const struct rtc_class_ops rtc_generic_ops = {
82	.read_time = aica_rtc_gettimeofday,
83	.set_time = aica_rtc_settimeofday,
84};
85
86static 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}
96arch_initcall(aica_time_init);
97