1/*
  2 * SPI Driver for Microchip MCP795 RTC
  3 *
  4 * Copyright (C) Josef Gajdusek <atx@atx.name>
  5 *
  6 * based on other Linux RTC drivers
  7 *
  8 * Device datasheet:
  9 * http://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
 10 *
 11 * This program is free software; you can redistribute it and/or modify
 12 * it under the terms of the GNU General Public License version 2 as
 13 * published by the Free Software Foundation.
 14 *
 15 */
 16
 17#include <linux/module.h>
 18#include <linux/kernel.h>
 19#include <linux/device.h>
 20#include <linux/printk.h>
 21#include <linux/spi/spi.h>
 22#include <linux/rtc.h>
 23#include <linux/of.h>
 24#include <linux/bcd.h>
 25#include <linux/delay.h>
 26
 27/* MCP795 Instructions, see datasheet table 3-1 */
 28#define MCP795_EEREAD	0x03
 29#define MCP795_EEWRITE	0x02
 30#define MCP795_EEWRDI	0x04
 31#define MCP795_EEWREN	0x06
 32#define MCP795_SRREAD	0x05
 33#define MCP795_SRWRITE	0x01
 34#define MCP795_READ	0x13
 35#define MCP795_WRITE	0x12
 36#define MCP795_UNLOCK	0x14
 37#define MCP795_IDWRITE	0x32
 38#define MCP795_IDREAD	0x33
 39#define MCP795_CLRWDT	0x44
 40#define MCP795_CLRRAM	0x54
 41
 42/* MCP795 RTCC registers, see datasheet table 4-1 */
 43#define MCP795_REG_SECONDS	0x01
 44#define MCP795_REG_DAY		0x04
 45#define MCP795_REG_MONTH	0x06
 46#define MCP795_REG_CONTROL	0x08
 47
 48#define MCP795_ST_BIT		BIT(7)
 49#define MCP795_24_BIT		BIT(6)
 50#define MCP795_LP_BIT		BIT(5)
 51#define MCP795_EXTOSC_BIT	BIT(3)
 52#define MCP795_OSCON_BIT	BIT(5)
 53
 54static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
 55{
 56	struct spi_device *spi = to_spi_device(dev);
 57	int ret;
 58	u8 tx[2];
 59
 60	tx[0] = MCP795_READ;
 61	tx[1] = addr;
 62	ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
 63
 64	if (ret)
 65		dev_err(dev, "Failed reading %d bytes from address %x.\n",
 66					count, addr);
 67
 68	return ret;
 69}
 70
 71static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
 72{
 73	struct spi_device *spi = to_spi_device(dev);
 74	int ret;
 75	u8 tx[2 + count];
 76
 77	tx[0] = MCP795_WRITE;
 78	tx[1] = addr;
 79	memcpy(&tx[2], data, count);
 80
 81	ret = spi_write(spi, tx, 2 + count);
 82
 83	if (ret)
 84		dev_err(dev, "Failed to write %d bytes to address %x.\n",
 85					count, addr);
 86
 87	return ret;
 88}
 89
 90static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
 91{
 92	int ret;
 93	u8 tmp;
 94
 95	ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
 96	if (ret)
 97		return ret;
 98
 99	if ((tmp & mask) != state) {
100		tmp = (tmp & ~mask) | state;
101		ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
102	}
103
104	return ret;
105}
106
107static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
108{
109	int retries = 5;
110	int ret;
111	u8 data;
112
113	ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
114	if (ret)
115		return ret;
116	ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
117	if (ret)
118		return ret;
119	*extosc = !!(data & MCP795_EXTOSC_BIT);
120	ret = mcp795_rtcc_set_bits(
121				dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
122	if (ret)
123		return ret;
124	/* wait for the OSCON bit to clear */
125	do {
126		usleep_range(700, 800);
127		ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
128		if (ret)
129			break;
130		if (!(data & MCP795_OSCON_BIT))
131			break;
132
133	} while (--retries);
134
135	return !retries ? -EIO : ret;
136}
137
138static int mcp795_start_oscillator(struct device *dev, bool *extosc)
139{
140	if (extosc) {
141		u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
142		int ret;
143
144		ret = mcp795_rtcc_set_bits(
145			dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
146		if (ret)
147			return ret;
148	}
149	return mcp795_rtcc_set_bits(
150			dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
151}
152
153static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
154{
155	int ret;
156	u8 data[7];
157	bool extosc;
158
159	/* Stop RTC and store current value of EXTOSC bit */
160	ret = mcp795_stop_oscillator(dev, &extosc);
161	if (ret)
162		return ret;
163
164	/* Read first, so we can leave config bits untouched */
165	ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
166
167	if (ret)
168		return ret;
169
170	data[0] = (data[0] & 0x80) | bin2bcd(tim->tm_sec);
171	data[1] = (data[1] & 0x80) | bin2bcd(tim->tm_min);
172	data[2] = bin2bcd(tim->tm_hour);
173	data[4] = bin2bcd(tim->tm_mday);
174	data[5] = (data[5] & MCP795_LP_BIT) | bin2bcd(tim->tm_mon + 1);
175
176	if (tim->tm_year > 100)
177		tim->tm_year -= 100;
178
179	data[6] = bin2bcd(tim->tm_year);
180
181	/* Always write the date and month using a separate Write command.
182	 * This is a workaround for a know silicon issue that some combinations
183	 * of date and month values may result in the date being reset to 1.
184	 */
185	ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
186	if (ret)
187		return ret;
188
189	ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
190	if (ret)
191		return ret;
192
193	/* Start back RTC and restore previous value of EXTOSC bit.
194	 * There is no need to clear EXTOSC bit when the previous value was 0
195	 * because it was already cleared when stopping the RTC oscillator.
196	 */
197	ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
198	if (ret)
199		return ret;
200
201	dev_dbg(dev, "Set mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
202			tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
203			tim->tm_hour, tim->tm_min, tim->tm_sec);
204
205	return 0;
206}
207
208static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
209{
210	int ret;
211	u8 data[7];
212
213	ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
214
215	if (ret)
216		return ret;
217
218	tim->tm_sec	= bcd2bin(data[0] & 0x7F);
219	tim->tm_min	= bcd2bin(data[1] & 0x7F);
220	tim->tm_hour	= bcd2bin(data[2] & 0x3F);
221	tim->tm_mday	= bcd2bin(data[4] & 0x3F);
222	tim->tm_mon	= bcd2bin(data[5] & 0x1F) - 1;
223	tim->tm_year	= bcd2bin(data[6]) + 100; /* Assume we are in 20xx */
224
225	dev_dbg(dev, "Read from mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
226				tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
227				tim->tm_hour, tim->tm_min, tim->tm_sec);
228
229	return rtc_valid_tm(tim);
230}
231
232static const struct rtc_class_ops mcp795_rtc_ops = {
233		.read_time = mcp795_read_time,
234		.set_time = mcp795_set_time
235};
236
237static int mcp795_probe(struct spi_device *spi)
238{
239	struct rtc_device *rtc;
240	int ret;
241
242	spi->mode = SPI_MODE_0;
243	spi->bits_per_word = 8;
244	ret = spi_setup(spi);
245	if (ret) {
246		dev_err(&spi->dev, "Unable to setup SPI\n");
247		return ret;
248	}
249
250	/* Start the oscillator but don't set the value of EXTOSC bit */
251	mcp795_start_oscillator(&spi->dev, NULL);
252	/* Clear the 12 hour mode flag*/
253	mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
254
255	rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
256					&mcp795_rtc_ops, THIS_MODULE);
257	if (IS_ERR(rtc))
258		return PTR_ERR(rtc);
259
260	spi_set_drvdata(spi, rtc);
261
262	return 0;
263}
264
265#ifdef CONFIG_OF
266static const struct of_device_id mcp795_of_match[] = {
267	{ .compatible = "maxim,mcp795" },
268	{ }
269};
270MODULE_DEVICE_TABLE(of, mcp795_of_match);
271#endif
272
273static struct spi_driver mcp795_driver = {
274		.driver = {
275				.name = "rtc-mcp795",
276				.of_match_table = of_match_ptr(mcp795_of_match),
277		},
278		.probe = mcp795_probe,
279};
280
281module_spi_driver(mcp795_driver);
282
283MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
284MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
285MODULE_LICENSE("GPL");
286MODULE_ALIAS("spi:mcp795");