1 // SPDX-License-Identifier: GPL-2.0-only
3 * SPI Driver for Microchip MCP795 RTC
5 * Copyright (C) Josef Gajdusek <atx@atx.name>
7 * based on other Linux RTC drivers
10 * https://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
13 #include <linux/module.h>
14 #include <linux/kernel.h>
15 #include <linux/device.h>
16 #include <linux/printk.h>
17 #include <linux/spi/spi.h>
18 #include <linux/rtc.h>
20 #include <linux/bcd.h>
21 #include <linux/delay.h>
23 /* MCP795 Instructions, see datasheet table 3-1 */
24 #define MCP795_EEREAD 0x03
25 #define MCP795_EEWRITE 0x02
26 #define MCP795_EEWRDI 0x04
27 #define MCP795_EEWREN 0x06
28 #define MCP795_SRREAD 0x05
29 #define MCP795_SRWRITE 0x01
30 #define MCP795_READ 0x13
31 #define MCP795_WRITE 0x12
32 #define MCP795_UNLOCK 0x14
33 #define MCP795_IDWRITE 0x32
34 #define MCP795_IDREAD 0x33
35 #define MCP795_CLRWDT 0x44
36 #define MCP795_CLRRAM 0x54
38 /* MCP795 RTCC registers, see datasheet table 4-1 */
39 #define MCP795_REG_SECONDS 0x01
40 #define MCP795_REG_DAY 0x04
41 #define MCP795_REG_MONTH 0x06
42 #define MCP795_REG_CONTROL 0x08
43 #define MCP795_REG_ALM0_SECONDS 0x0C
44 #define MCP795_REG_ALM0_DAY 0x0F
46 #define MCP795_ST_BIT BIT(7)
47 #define MCP795_24_BIT BIT(6)
48 #define MCP795_LP_BIT BIT(5)
49 #define MCP795_EXTOSC_BIT BIT(3)
50 #define MCP795_OSCON_BIT BIT(5)
51 #define MCP795_ALM0_BIT BIT(4)
52 #define MCP795_ALM1_BIT BIT(5)
53 #define MCP795_ALM0IF_BIT BIT(3)
54 #define MCP795_ALM0C0_BIT BIT(4)
55 #define MCP795_ALM0C1_BIT BIT(5)
56 #define MCP795_ALM0C2_BIT BIT(6)
58 #define SEC_PER_DAY (24 * 60 * 60)
60 static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
62 struct spi_device *spi = to_spi_device(dev);
68 ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
71 dev_err(dev, "Failed reading %d bytes from address %x.\n",
77 static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
79 struct spi_device *spi = to_spi_device(dev);
85 memcpy(&tx[2], data, count);
87 ret = spi_write(spi, tx, 2 + count);
90 dev_err(dev, "Failed to write %d bytes to address %x.\n",
96 static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
101 ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
105 if ((tmp & mask) != state) {
106 tmp = (tmp & ~mask) | state;
107 ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
113 static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
119 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
122 ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
125 *extosc = !!(data & MCP795_EXTOSC_BIT);
126 ret = mcp795_rtcc_set_bits(
127 dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
130 /* wait for the OSCON bit to clear */
132 usleep_range(700, 800);
133 ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
136 if (!(data & MCP795_OSCON_BIT))
141 return !retries ? -EIO : ret;
144 static int mcp795_start_oscillator(struct device *dev, bool *extosc)
147 u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
150 ret = mcp795_rtcc_set_bits(
151 dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
155 return mcp795_rtcc_set_bits(
156 dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
159 /* Enable or disable Alarm 0 in RTC */
160 static int mcp795_update_alarm(struct device *dev, bool enable)
164 dev_dbg(dev, "%s alarm\n", enable ? "Enable" : "Disable");
167 /* clear ALM0IF (Alarm 0 Interrupt Flag) bit */
168 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_ALM0_DAY,
169 MCP795_ALM0IF_BIT, 0);
173 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
174 MCP795_ALM0_BIT, MCP795_ALM0_BIT);
176 /* disable alarm 0 and alarm 1 */
177 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
178 MCP795_ALM0_BIT | MCP795_ALM1_BIT, 0);
183 static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
189 /* Stop RTC and store current value of EXTOSC bit */
190 ret = mcp795_stop_oscillator(dev, &extosc);
194 /* Read first, so we can leave config bits untouched */
195 ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
200 data[0] = (data[0] & 0x80) | bin2bcd(tim->tm_sec);
201 data[1] = (data[1] & 0x80) | bin2bcd(tim->tm_min);
202 data[2] = bin2bcd(tim->tm_hour);
203 data[3] = (data[3] & 0xF8) | bin2bcd(tim->tm_wday + 1);
204 data[4] = bin2bcd(tim->tm_mday);
205 data[5] = (data[5] & MCP795_LP_BIT) | bin2bcd(tim->tm_mon + 1);
207 if (tim->tm_year > 100)
210 data[6] = bin2bcd(tim->tm_year);
212 /* Always write the date and month using a separate Write command.
213 * This is a workaround for a know silicon issue that some combinations
214 * of date and month values may result in the date being reset to 1.
216 ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
220 ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
224 /* Start back RTC and restore previous value of EXTOSC bit.
225 * There is no need to clear EXTOSC bit when the previous value was 0
226 * because it was already cleared when stopping the RTC oscillator.
228 ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
232 dev_dbg(dev, "Set mcp795: %ptR\n", tim);
237 static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
242 ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
247 tim->tm_sec = bcd2bin(data[0] & 0x7F);
248 tim->tm_min = bcd2bin(data[1] & 0x7F);
249 tim->tm_hour = bcd2bin(data[2] & 0x3F);
250 tim->tm_wday = bcd2bin(data[3] & 0x07) - 1;
251 tim->tm_mday = bcd2bin(data[4] & 0x3F);
252 tim->tm_mon = bcd2bin(data[5] & 0x1F) - 1;
253 tim->tm_year = bcd2bin(data[6]) + 100; /* Assume we are in 20xx */
255 dev_dbg(dev, "Read from mcp795: %ptR\n", tim);
260 static int mcp795_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
262 struct rtc_time now_tm;
268 /* Read current time from RTC hardware */
269 ret = mcp795_read_time(dev, &now_tm);
272 /* Get the number of seconds since 1970 */
273 now = rtc_tm_to_time64(&now_tm);
274 later = rtc_tm_to_time64(&alm->time);
277 /* make sure alarm fires within the next one year */
279 (SEC_PER_DAY * (365 + is_leap_year(alm->time.tm_year))))
282 ret = mcp795_update_alarm(dev, false);
285 /* Read registers, so we can leave configuration bits untouched */
286 ret = mcp795_rtcc_read(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
290 alm->time.tm_year = -1;
291 alm->time.tm_isdst = -1;
292 alm->time.tm_yday = -1;
294 tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);
295 tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);
296 tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);
297 tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);
298 /* set alarm match: seconds, minutes, hour, day, date and month */
299 tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT | MCP795_ALM0C0_BIT);
300 tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);
301 tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);
303 ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
307 /* enable alarm if requested */
309 ret = mcp795_update_alarm(dev, true);
312 dev_dbg(dev, "Alarm IRQ armed\n");
314 dev_dbg(dev, "Set alarm: %ptRdr(%d) %ptRt\n",
315 &alm->time, alm->time.tm_wday, &alm->time);
319 static int mcp795_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
324 ret = mcp795_rtcc_read(
325 dev, MCP795_REG_ALM0_SECONDS, data, sizeof(data));
329 alm->time.tm_sec = bcd2bin(data[0] & 0x7F);
330 alm->time.tm_min = bcd2bin(data[1] & 0x7F);
331 alm->time.tm_hour = bcd2bin(data[2] & 0x1F);
332 alm->time.tm_wday = bcd2bin(data[3] & 0x07) - 1;
333 alm->time.tm_mday = bcd2bin(data[4] & 0x3F);
334 alm->time.tm_mon = bcd2bin(data[5] & 0x1F) - 1;
335 alm->time.tm_year = -1;
336 alm->time.tm_isdst = -1;
337 alm->time.tm_yday = -1;
339 dev_dbg(dev, "Read alarm: %ptRdr(%d) %ptRt\n",
340 &alm->time, alm->time.tm_wday, &alm->time);
344 static int mcp795_alarm_irq_enable(struct device *dev, unsigned int enabled)
346 return mcp795_update_alarm(dev, !!enabled);
349 static irqreturn_t mcp795_irq(int irq, void *data)
351 struct spi_device *spi = data;
352 struct rtc_device *rtc = spi_get_drvdata(spi);
353 struct mutex *lock = &rtc->ops_lock;
359 * There is no need to clear ALM0IF (Alarm 0 Interrupt Flag) bit,
360 * because it is done every time when alarm is enabled.
362 ret = mcp795_update_alarm(&spi->dev, false);
365 "Failed to disable alarm in IRQ (ret=%d)\n", ret);
366 rtc_update_irq(rtc, 1, RTC_AF | RTC_IRQF);
373 static const struct rtc_class_ops mcp795_rtc_ops = {
374 .read_time = mcp795_read_time,
375 .set_time = mcp795_set_time,
376 .read_alarm = mcp795_read_alarm,
377 .set_alarm = mcp795_set_alarm,
378 .alarm_irq_enable = mcp795_alarm_irq_enable
381 static int mcp795_probe(struct spi_device *spi)
383 struct rtc_device *rtc;
386 spi->mode = SPI_MODE_0;
387 spi->bits_per_word = 8;
388 ret = spi_setup(spi);
390 dev_err(&spi->dev, "Unable to setup SPI\n");
394 /* Start the oscillator but don't set the value of EXTOSC bit */
395 mcp795_start_oscillator(&spi->dev, NULL);
396 /* Clear the 12 hour mode flag*/
397 mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
399 rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
400 &mcp795_rtc_ops, THIS_MODULE);
404 spi_set_drvdata(spi, rtc);
407 dev_dbg(&spi->dev, "Alarm support enabled\n");
409 /* Clear any pending alarm (ALM0IF bit) before requesting
412 mcp795_rtcc_set_bits(&spi->dev, MCP795_REG_ALM0_DAY,
413 MCP795_ALM0IF_BIT, 0);
414 ret = devm_request_threaded_irq(&spi->dev, spi->irq, NULL,
415 mcp795_irq, IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
416 dev_name(&rtc->dev), spi);
418 dev_err(&spi->dev, "Failed to request IRQ: %d: %d\n",
421 device_init_wakeup(&spi->dev, true);
427 static const struct of_device_id mcp795_of_match[] = {
428 { .compatible = "maxim,mcp795" },
431 MODULE_DEVICE_TABLE(of, mcp795_of_match);
434 static struct spi_driver mcp795_driver = {
436 .name = "rtc-mcp795",
437 .of_match_table = of_match_ptr(mcp795_of_match),
439 .probe = mcp795_probe,
442 module_spi_driver(mcp795_driver);
444 MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
445 MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
446 MODULE_LICENSE("GPL");
447 MODULE_ALIAS("spi:mcp795");