1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * SPI Driver for Microchip MCP795 RTC
4 *
5 * Copyright (C) Josef Gajdusek <atx@atx.name>
6 *
7 * based on other Linux RTC drivers
8 *
9 * Device datasheet:
10 * https://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
11 */
12
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>
19 #include <linux/of.h>
20 #include <linux/bcd.h>
21 #include <linux/delay.h>
22
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
37
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
45
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)
57
58 #define SEC_PER_DAY (24 * 60 * 60)
59
mcp795_rtcc_read(struct device * dev,u8 addr,u8 * buf,u8 count)60 static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
61 {
62 struct spi_device *spi = to_spi_device(dev);
63 int ret;
64 u8 tx[2];
65
66 tx[0] = MCP795_READ;
67 tx[1] = addr;
68 ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
69
70 if (ret)
71 dev_err(dev, "Failed reading %d bytes from address %x.\n",
72 count, addr);
73
74 return ret;
75 }
76
mcp795_rtcc_write(struct device * dev,u8 addr,u8 * data,u8 count)77 static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
78 {
79 struct spi_device *spi = to_spi_device(dev);
80 int ret;
81 u8 tx[257];
82
83 tx[0] = MCP795_WRITE;
84 tx[1] = addr;
85 memcpy(&tx[2], data, count);
86
87 ret = spi_write(spi, tx, 2 + count);
88
89 if (ret)
90 dev_err(dev, "Failed to write %d bytes to address %x.\n",
91 count, addr);
92
93 return ret;
94 }
95
mcp795_rtcc_set_bits(struct device * dev,u8 addr,u8 mask,u8 state)96 static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
97 {
98 int ret;
99 u8 tmp;
100
101 ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
102 if (ret)
103 return ret;
104
105 if ((tmp & mask) != state) {
106 tmp = (tmp & ~mask) | state;
107 ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
108 }
109
110 return ret;
111 }
112
mcp795_stop_oscillator(struct device * dev,bool * extosc)113 static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
114 {
115 int retries = 5;
116 int ret;
117 u8 data;
118
119 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
120 if (ret)
121 return ret;
122 ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
123 if (ret)
124 return ret;
125 *extosc = !!(data & MCP795_EXTOSC_BIT);
126 ret = mcp795_rtcc_set_bits(
127 dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
128 if (ret)
129 return ret;
130 /* wait for the OSCON bit to clear */
131 do {
132 usleep_range(700, 800);
133 ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
134 if (ret)
135 break;
136 if (!(data & MCP795_OSCON_BIT))
137 break;
138
139 } while (--retries);
140
141 return !retries ? -EIO : ret;
142 }
143
mcp795_start_oscillator(struct device * dev,bool * extosc)144 static int mcp795_start_oscillator(struct device *dev, bool *extosc)
145 {
146 if (extosc) {
147 u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
148 int ret;
149
150 ret = mcp795_rtcc_set_bits(
151 dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
152 if (ret)
153 return ret;
154 }
155 return mcp795_rtcc_set_bits(
156 dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
157 }
158
159 /* Enable or disable Alarm 0 in RTC */
mcp795_update_alarm(struct device * dev,bool enable)160 static int mcp795_update_alarm(struct device *dev, bool enable)
161 {
162 int ret;
163
164 dev_dbg(dev, "%s alarm\n", enable ? "Enable" : "Disable");
165
166 if (enable) {
167 /* clear ALM0IF (Alarm 0 Interrupt Flag) bit */
168 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_ALM0_DAY,
169 MCP795_ALM0IF_BIT, 0);
170 if (ret)
171 return ret;
172 /* enable alarm 0 */
173 ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
174 MCP795_ALM0_BIT, MCP795_ALM0_BIT);
175 } else {
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);
179 }
180 return ret;
181 }
182
mcp795_set_time(struct device * dev,struct rtc_time * tim)183 static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
184 {
185 int ret;
186 u8 data[7];
187 bool extosc;
188
189 /* Stop RTC and store current value of EXTOSC bit */
190 ret = mcp795_stop_oscillator(dev, &extosc);
191 if (ret)
192 return ret;
193
194 /* Read first, so we can leave config bits untouched */
195 ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
196
197 if (ret)
198 return ret;
199
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);
206
207 if (tim->tm_year > 100)
208 tim->tm_year -= 100;
209
210 data[6] = bin2bcd(tim->tm_year);
211
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.
215 */
216 ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
217 if (ret)
218 return ret;
219
220 ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
221 if (ret)
222 return ret;
223
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.
227 */
228 ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
229 if (ret)
230 return ret;
231
232 dev_dbg(dev, "Set mcp795: %ptR\n", tim);
233
234 return 0;
235 }
236
mcp795_read_time(struct device * dev,struct rtc_time * tim)237 static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
238 {
239 int ret;
240 u8 data[7];
241
242 ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
243
244 if (ret)
245 return ret;
246
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 */
254
255 dev_dbg(dev, "Read from mcp795: %ptR\n", tim);
256
257 return 0;
258 }
259
mcp795_set_alarm(struct device * dev,struct rtc_wkalrm * alm)260 static int mcp795_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
261 {
262 struct rtc_time now_tm;
263 time64_t now;
264 time64_t later;
265 u8 tmp[6];
266 int ret;
267
268 /* Read current time from RTC hardware */
269 ret = mcp795_read_time(dev, &now_tm);
270 if (ret)
271 return ret;
272 /* Get the number of seconds since 1970 */
273 now = rtc_tm_to_time64(&now_tm);
274 later = rtc_tm_to_time64(&alm->time);
275 if (later <= now)
276 return -EINVAL;
277 /* make sure alarm fires within the next one year */
278 if ((later - now) >=
279 (SEC_PER_DAY * (365 + is_leap_year(alm->time.tm_year))))
280 return -EDOM;
281 /* disable alarm */
282 ret = mcp795_update_alarm(dev, false);
283 if (ret)
284 return ret;
285 /* Read registers, so we can leave configuration bits untouched */
286 ret = mcp795_rtcc_read(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
287 if (ret)
288 return ret;
289
290 alm->time.tm_year = -1;
291 alm->time.tm_isdst = -1;
292 alm->time.tm_yday = -1;
293
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);
302
303 ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
304 if (ret)
305 return ret;
306
307 /* enable alarm if requested */
308 if (alm->enabled) {
309 ret = mcp795_update_alarm(dev, true);
310 if (ret)
311 return ret;
312 dev_dbg(dev, "Alarm IRQ armed\n");
313 }
314 dev_dbg(dev, "Set alarm: %ptRdr(%d) %ptRt\n",
315 &alm->time, alm->time.tm_wday, &alm->time);
316 return 0;
317 }
318
mcp795_read_alarm(struct device * dev,struct rtc_wkalrm * alm)319 static int mcp795_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
320 {
321 u8 data[6];
322 int ret;
323
324 ret = mcp795_rtcc_read(
325 dev, MCP795_REG_ALM0_SECONDS, data, sizeof(data));
326 if (ret)
327 return ret;
328
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;
338
339 dev_dbg(dev, "Read alarm: %ptRdr(%d) %ptRt\n",
340 &alm->time, alm->time.tm_wday, &alm->time);
341 return 0;
342 }
343
mcp795_alarm_irq_enable(struct device * dev,unsigned int enabled)344 static int mcp795_alarm_irq_enable(struct device *dev, unsigned int enabled)
345 {
346 return mcp795_update_alarm(dev, !!enabled);
347 }
348
mcp795_irq(int irq,void * data)349 static irqreturn_t mcp795_irq(int irq, void *data)
350 {
351 struct spi_device *spi = data;
352 struct rtc_device *rtc = spi_get_drvdata(spi);
353 int ret;
354
355 rtc_lock(rtc);
356
357 /* Disable alarm.
358 * There is no need to clear ALM0IF (Alarm 0 Interrupt Flag) bit,
359 * because it is done every time when alarm is enabled.
360 */
361 ret = mcp795_update_alarm(&spi->dev, false);
362 if (ret)
363 dev_err(&spi->dev,
364 "Failed to disable alarm in IRQ (ret=%d)\n", ret);
365 rtc_update_irq(rtc, 1, RTC_AF | RTC_IRQF);
366
367 rtc_unlock(rtc);
368
369 return IRQ_HANDLED;
370 }
371
372 static const struct rtc_class_ops mcp795_rtc_ops = {
373 .read_time = mcp795_read_time,
374 .set_time = mcp795_set_time,
375 .read_alarm = mcp795_read_alarm,
376 .set_alarm = mcp795_set_alarm,
377 .alarm_irq_enable = mcp795_alarm_irq_enable
378 };
379
mcp795_probe(struct spi_device * spi)380 static int mcp795_probe(struct spi_device *spi)
381 {
382 struct rtc_device *rtc;
383 int ret;
384
385 spi->mode = SPI_MODE_0;
386 spi->bits_per_word = 8;
387 ret = spi_setup(spi);
388 if (ret) {
389 dev_err(&spi->dev, "Unable to setup SPI\n");
390 return ret;
391 }
392
393 /* Start the oscillator but don't set the value of EXTOSC bit */
394 mcp795_start_oscillator(&spi->dev, NULL);
395 /* Clear the 12 hour mode flag*/
396 mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
397
398 rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
399 &mcp795_rtc_ops, THIS_MODULE);
400 if (IS_ERR(rtc))
401 return PTR_ERR(rtc);
402
403 spi_set_drvdata(spi, rtc);
404
405 if (spi->irq > 0) {
406 dev_dbg(&spi->dev, "Alarm support enabled\n");
407
408 /* Clear any pending alarm (ALM0IF bit) before requesting
409 * the interrupt.
410 */
411 mcp795_rtcc_set_bits(&spi->dev, MCP795_REG_ALM0_DAY,
412 MCP795_ALM0IF_BIT, 0);
413 ret = devm_request_threaded_irq(&spi->dev, spi->irq, NULL,
414 mcp795_irq, IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
415 dev_name(&rtc->dev), spi);
416 if (ret)
417 dev_err(&spi->dev, "Failed to request IRQ: %d: %d\n",
418 spi->irq, ret);
419 else
420 device_init_wakeup(&spi->dev, true);
421 }
422 return 0;
423 }
424
425 #ifdef CONFIG_OF
426 static const struct of_device_id mcp795_of_match[] = {
427 { .compatible = "maxim,mcp795" },
428 { }
429 };
430 MODULE_DEVICE_TABLE(of, mcp795_of_match);
431 #endif
432
433 static const struct spi_device_id mcp795_spi_ids[] = {
434 { .name = "mcp795" },
435 { }
436 };
437 MODULE_DEVICE_TABLE(spi, mcp795_spi_ids);
438
439 static struct spi_driver mcp795_driver = {
440 .driver = {
441 .name = "rtc-mcp795",
442 .of_match_table = of_match_ptr(mcp795_of_match),
443 },
444 .probe = mcp795_probe,
445 .id_table = mcp795_spi_ids,
446 };
447
448 module_spi_driver(mcp795_driver);
449
450 MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
451 MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
452 MODULE_LICENSE("GPL");
453