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
 25/* MCP795 Instructions, see datasheet table 3-1 */
 26#define MCP795_EEREAD	0x03
 27#define MCP795_EEWRITE	0x02
 28#define MCP795_EEWRDI	0x04
 29#define MCP795_EEWREN	0x06
 30#define MCP795_SRREAD	0x05
 31#define MCP795_SRWRITE	0x01
 32#define MCP795_READ		0x13
 33#define MCP795_WRITE	0x12
 34#define MCP795_UNLOCK	0x14
 35#define MCP795_IDWRITE	0x32
 36#define MCP795_IDREAD	0x33
 37#define MCP795_CLRWDT	0x44
 38#define MCP795_CLRRAM	0x54
 39
 40#define MCP795_ST_BIT	0x80
 41#define MCP795_24_BIT	0x40
 42
 43static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
 44{
 45	struct spi_device *spi = to_spi_device(dev);
 46	int ret;
 47	u8 tx[2];
 48
 49	tx[0] = MCP795_READ;
 50	tx[1] = addr;
 51	ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
 52
 53	if (ret)
 54		dev_err(dev, "Failed reading %d bytes from address %x.\n",
 55					count, addr);
 56
 57	return ret;
 58}
 59
 60static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
 61{
 62	struct spi_device *spi = to_spi_device(dev);
 63	int ret;
 64	u8 tx[2 + count];
 65
 66	tx[0] = MCP795_WRITE;
 67	tx[1] = addr;
 68	memcpy(&tx[2], data, count);
 69
 70	ret = spi_write(spi, tx, 2 + count);
 71
 72	if (ret)
 73		dev_err(dev, "Failed to write %d bytes to address %x.\n",
 74					count, addr);
 75
 76	return ret;
 77}
 78
 79static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
 80{
 81	int ret;
 82	u8 tmp;
 83
 84	ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
 85	if (ret)
 86		return ret;
 87
 88	if ((tmp & mask) != state) {
 89		tmp = (tmp & ~mask) | state;
 90		ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
 91	}
 92
 93	return ret;
 94}
 95
 96static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
 97{
 98	int ret;
 99	u8 data[7];
100
101	/* Read first, so we can leave config bits untouched */
102	ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
103
104	if (ret)
105		return ret;
106
107	data[0] = (data[0] & 0x80) | ((tim->tm_sec / 10) << 4) | (tim->tm_sec % 10);
108	data[1] = (data[1] & 0x80) | ((tim->tm_min / 10) << 4) | (tim->tm_min % 10);
109	data[2] = ((tim->tm_hour / 10) << 4) | (tim->tm_hour % 10);
110	data[4] = ((tim->tm_mday / 10) << 4) | ((tim->tm_mday) % 10);
111	data[5] = (data[5] & 0x10) | (tim->tm_mon / 10) | (tim->tm_mon % 10);
112
113	if (tim->tm_year > 100)
114		tim->tm_year -= 100;
115
116	data[6] = ((tim->tm_year / 10) << 4) | (tim->tm_year % 10);
117
118	ret = mcp795_rtcc_write(dev, 0x01, data, sizeof(data));
119
120	if (ret)
121		return ret;
122
123	dev_dbg(dev, "Set mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
124			tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
125			tim->tm_hour, tim->tm_min, tim->tm_sec);
126
127	return 0;
128}
129
130static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
131{
132	int ret;
133	u8 data[7];
134
135	ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
136
137	if (ret)
138		return ret;
139
140	tim->tm_sec		= ((data[0] & 0x70) >> 4) * 10 + (data[0] & 0x0f);
141	tim->tm_min		= ((data[1] & 0x70) >> 4) * 10 + (data[1] & 0x0f);
142	tim->tm_hour	= ((data[2] & 0x30) >> 4) * 10 + (data[2] & 0x0f);
143	tim->tm_mday	= ((data[4] & 0x30) >> 4) * 10 + (data[4] & 0x0f);
144	tim->tm_mon		= ((data[5] & 0x10) >> 4) * 10 + (data[5] & 0x0f);
145	tim->tm_year	= ((data[6] & 0xf0) >> 4) * 10 + (data[6] & 0x0f) + 100; /* Assume we are in 20xx */
146
147	dev_dbg(dev, "Read from mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
148				tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
149				tim->tm_hour, tim->tm_min, tim->tm_sec);
150
151	return rtc_valid_tm(tim);
152}
153
154static struct rtc_class_ops mcp795_rtc_ops = {
155		.read_time = mcp795_read_time,
156		.set_time = mcp795_set_time
157};
158
159static int mcp795_probe(struct spi_device *spi)
160{
161	struct rtc_device *rtc;
162	int ret;
163
164	spi->mode = SPI_MODE_0;
165	spi->bits_per_word = 8;
166	ret = spi_setup(spi);
167	if (ret) {
168		dev_err(&spi->dev, "Unable to setup SPI\n");
169		return ret;
170	}
171
172	/* Start the oscillator */
173	mcp795_rtcc_set_bits(&spi->dev, 0x01, MCP795_ST_BIT, MCP795_ST_BIT);
174	/* Clear the 12 hour mode flag*/
175	mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
176
177	rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
178								&mcp795_rtc_ops, THIS_MODULE);
179	if (IS_ERR(rtc))
180		return PTR_ERR(rtc);
181
182	spi_set_drvdata(spi, rtc);
183
184	return 0;
185}
186
187#ifdef CONFIG_OF
188static const struct of_device_id mcp795_of_match[] = {
189	{ .compatible = "maxim,mcp795" },
190	{ }
191};
192MODULE_DEVICE_TABLE(of, mcp795_of_match);
193#endif
194
195static struct spi_driver mcp795_driver = {
196		.driver = {
197				.name = "rtc-mcp795",
198				.of_match_table = of_match_ptr(mcp795_of_match),
199		},
200		.probe = mcp795_probe,
201};
202
203module_spi_driver(mcp795_driver);
204
205MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
206MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
207MODULE_LICENSE("GPL");
208MODULE_ALIAS("spi:mcp795");