rtc-spacemit-p1.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Driver for the RTC found in the SpacemiT P1 PMIC
  4 *
  5 * Copyright (C) 2025 by RISCstar Solutions Corporation.  All rights reserved.
  6 */
  7
  8#include <linux/bits.h>
  9#include <linux/device.h>
 10#include <linux/module.h>
 11#include <linux/platform_device.h>
 12#include <linux/regmap.h>
 13#include <linux/rtc.h>
 14
 15#define MOD_NAME	"spacemit-p1-rtc"
 16
 17/*
 18 * Six consecutive 1-byte registers hold the seconds, minutes, hours,
 19 * day-of-month, month, and year (respectively).
 20 *
 21 * The range of values in these registers is:
 22 *    seconds	0-59
 23 *    minutes	0-59
 24 *    hours	0-59
 25 *    day	0-30 (struct tm is 1-31)
 26 *    month	0-11
 27 *    year	years since 2000 (struct tm is since 1900)
 28 *
 29 * Note that the day and month must be converted after reading and
 30 * before writing.
 31 */
 32#define RTC_TIME		0x0d	/* Offset of the seconds register */
 33
 34#define RTC_CTRL		0x1d
 35#define RTC_EN		BIT(2)
 36
 37/* Number of attempts to read a consistent time stamp before giving up */
 38#define RTC_READ_TRIES		20	/* At least 1 */
 39
 40struct p1_rtc {
 41	struct regmap *regmap;
 42	struct rtc_device *rtc;
 43};
 44
 45/*
 46 * The P1 hardware documentation states that the register values are
 47 * latched to ensure a consistent time snapshot within the registers,
 48 * but these are in fact unstable due to a bug in the hardware design.
 49 * So we loop until we get two identical readings.
 50 */
 51static int p1_rtc_read_time(struct device *dev, struct rtc_time *t)
 52{
 53	struct p1_rtc *p1 = dev_get_drvdata(dev);
 54	struct regmap *regmap = p1->regmap;
 55	u32 count = RTC_READ_TRIES;
 56	u8 seconds;
 57	u8 time[6];
 58	int ret;
 59
 60	if (!regmap_test_bits(regmap, RTC_CTRL, RTC_EN))
 61		return -EINVAL;		/* RTC is disabled */
 62
 63	ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
 64	if (ret)
 65		return ret;
 66
 67	do {
 68		seconds = time[0];
 69		ret = regmap_bulk_read(regmap, RTC_TIME, time, sizeof(time));
 70		if (ret)
 71			return ret;
 72	} while (time[0] != seconds && --count);
 73
 74	if (!count)
 75		return -EIO;		/* Unable to get a consistent result */
 76
 77	t->tm_sec = time[0] & GENMASK(5, 0);
 78	t->tm_min = time[1] & GENMASK(5, 0);
 79	t->tm_hour = time[2] & GENMASK(4, 0);
 80	t->tm_mday = (time[3] & GENMASK(4, 0)) + 1;
 81	t->tm_mon = time[4] & GENMASK(3, 0);
 82	t->tm_year = (time[5] & GENMASK(5, 0)) + 100;
 83
 84	return 0;
 85}
 86
 87/*
 88 * The P1 hardware documentation states that values in the registers are
 89 * latched so when written they represent a consistent time snapshot.
 90 * Nevertheless, this is not guaranteed by the implementation, so we must
 91 * disable the RTC while updating it.
 92 */
 93static int p1_rtc_set_time(struct device *dev, struct rtc_time *t)
 94{
 95	struct p1_rtc *p1 = dev_get_drvdata(dev);
 96	struct regmap *regmap = p1->regmap;
 97	u8 time[6];
 98	int ret;
 99
100	time[0] = t->tm_sec;
101	time[1] = t->tm_min;
102	time[2] = t->tm_hour;
103	time[3] = t->tm_mday - 1;
104	time[4] = t->tm_mon;
105	time[5] = t->tm_year - 100;
106
107	/* Disable the RTC to update; re-enable again when done */
108	ret = regmap_clear_bits(regmap, RTC_CTRL, RTC_EN);
109	if (ret)
110		return ret;
111
112	/* If something goes wrong, leave the RTC disabled */
113	ret = regmap_bulk_write(regmap, RTC_TIME, time, sizeof(time));
114	if (ret)
115		return ret;
116
117	return regmap_set_bits(regmap, RTC_CTRL, RTC_EN);
118}
119
120static const struct rtc_class_ops p1_rtc_class_ops = {
121	.read_time = p1_rtc_read_time,
122	.set_time = p1_rtc_set_time,
123};
124
125static int p1_rtc_probe(struct platform_device *pdev)
126{
127	struct device *dev = &pdev->dev;
128	struct rtc_device *rtc;
129	struct p1_rtc *p1;
130
131	p1 = devm_kzalloc(dev, sizeof(*p1), GFP_KERNEL);
132	if (!p1)
133		return -ENOMEM;
134	dev_set_drvdata(dev, p1);
135
136	p1->regmap = dev_get_regmap(dev->parent, NULL);
137	if (!p1->regmap)
138		return dev_err_probe(dev, -ENODEV, "failed to get regmap\n");
139
140	rtc = devm_rtc_allocate_device(dev);
141	if (IS_ERR(rtc))
142		return dev_err_probe(dev, PTR_ERR(rtc),
143				     "error allocating device\n");
144	p1->rtc = rtc;
145
146	rtc->ops = &p1_rtc_class_ops;
147	rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
148	rtc->range_max = RTC_TIMESTAMP_END_2063;
149
150	clear_bit(RTC_FEATURE_ALARM, rtc->features);
151	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
152
153	return devm_rtc_register_device(rtc);
154}
155
156static struct platform_driver p1_rtc_driver = {
157	.probe = p1_rtc_probe,
158	.driver = {
159		.name = MOD_NAME,
160	},
161};
162
163module_platform_driver(p1_rtc_driver);
164
165MODULE_DESCRIPTION("SpacemiT P1 RTC driver");
166MODULE_LICENSE("GPL");
167MODULE_ALIAS("platform:" MOD_NAME);