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/*
* SPI Driver for Microchip MCP795 RTC
*
* Copyright (C) Josef Gajdusek <atx@atx.name>
*
* based on other Linux RTC drivers
*
* Device datasheet:
* http://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/printk.h>
#include <linux/spi/spi.h>
#include <linux/rtc.h>
#include <linux/of.h>
#include <linux/bcd.h>
#include <linux/delay.h>
/* MCP795 Instructions, see datasheet table 3-1 */
#define MCP795_EEREAD 0x03
#define MCP795_EEWRITE 0x02
#define MCP795_EEWRDI 0x04
#define MCP795_EEWREN 0x06
#define MCP795_SRREAD 0x05
#define MCP795_SRWRITE 0x01
#define MCP795_READ 0x13
#define MCP795_WRITE 0x12
#define MCP795_UNLOCK 0x14
#define MCP795_IDWRITE 0x32
#define MCP795_IDREAD 0x33
#define MCP795_CLRWDT 0x44
#define MCP795_CLRRAM 0x54
/* MCP795 RTCC registers, see datasheet table 4-1 */
#define MCP795_REG_SECONDS 0x01
#define MCP795_REG_DAY 0x04
#define MCP795_REG_MONTH 0x06
#define MCP795_REG_CONTROL 0x08
#define MCP795_ST_BIT BIT(7)
#define MCP795_24_BIT BIT(6)
#define MCP795_LP_BIT BIT(5)
#define MCP795_EXTOSC_BIT BIT(3)
#define MCP795_OSCON_BIT BIT(5)
static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
{
struct spi_device *spi = to_spi_device(dev);
int ret;
u8 tx[2];
tx[0] = MCP795_READ;
tx[1] = addr;
ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
if (ret)
dev_err(dev, "Failed reading %d bytes from address %x.\n",
count, addr);
return ret;
}
static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
{
struct spi_device *spi = to_spi_device(dev);
int ret;
u8 tx[2 + count];
tx[0] = MCP795_WRITE;
tx[1] = addr;
memcpy(&tx[2], data, count);
ret = spi_write(spi, tx, 2 + count);
if (ret)
dev_err(dev, "Failed to write %d bytes to address %x.\n",
count, addr);
return ret;
}
static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
{
int ret;
u8 tmp;
ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
if (ret)
return ret;
if ((tmp & mask) != state) {
tmp = (tmp & ~mask) | state;
ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
}
return ret;
}
static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
{
int retries = 5;
int ret;
u8 data;
ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
if (ret)
return ret;
ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
if (ret)
return ret;
*extosc = !!(data & MCP795_EXTOSC_BIT);
ret = mcp795_rtcc_set_bits(
dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
if (ret)
return ret;
/* wait for the OSCON bit to clear */
do {
usleep_range(700, 800);
ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
if (ret)
break;
if (!(data & MCP795_OSCON_BIT))
break;
} while (--retries);
return !retries ? -EIO : ret;
}
static int mcp795_start_oscillator(struct device *dev, bool *extosc)
{
if (extosc) {
u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
int ret;
ret = mcp795_rtcc_set_bits(
dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
if (ret)
return ret;
}
return mcp795_rtcc_set_bits(
dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
}
static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
{
int ret;
u8 data[7];
bool extosc;
/* Stop RTC and store current value of EXTOSC bit */
ret = mcp795_stop_oscillator(dev, &extosc);
if (ret)
return ret;
/* Read first, so we can leave config bits untouched */
ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
if (ret)
return ret;
data[0] = (data[0] & 0x80) | bin2bcd(tim->tm_sec);
data[1] = (data[1] & 0x80) | bin2bcd(tim->tm_min);
data[2] = bin2bcd(tim->tm_hour);
data[4] = bin2bcd(tim->tm_mday);
data[5] = (data[5] & MCP795_LP_BIT) | bin2bcd(tim->tm_mon + 1);
if (tim->tm_year > 100)
tim->tm_year -= 100;
data[6] = bin2bcd(tim->tm_year);
/* Always write the date and month using a separate Write command.
* This is a workaround for a know silicon issue that some combinations
* of date and month values may result in the date being reset to 1.
*/
ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
if (ret)
return ret;
ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
if (ret)
return ret;
/* Start back RTC and restore previous value of EXTOSC bit.
* There is no need to clear EXTOSC bit when the previous value was 0
* because it was already cleared when stopping the RTC oscillator.
*/
ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
if (ret)
return ret;
dev_dbg(dev, "Set mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
tim->tm_hour, tim->tm_min, tim->tm_sec);
return 0;
}
static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
{
int ret;
u8 data[7];
ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
if (ret)
return ret;
tim->tm_sec = bcd2bin(data[0] & 0x7F);
tim->tm_min = bcd2bin(data[1] & 0x7F);
tim->tm_hour = bcd2bin(data[2] & 0x3F);
tim->tm_mday = bcd2bin(data[4] & 0x3F);
tim->tm_mon = bcd2bin(data[5] & 0x1F) - 1;
tim->tm_year = bcd2bin(data[6]) + 100; /* Assume we are in 20xx */
dev_dbg(dev, "Read from mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
tim->tm_hour, tim->tm_min, tim->tm_sec);
return rtc_valid_tm(tim);
}
static const struct rtc_class_ops mcp795_rtc_ops = {
.read_time = mcp795_read_time,
.set_time = mcp795_set_time
};
static int mcp795_probe(struct spi_device *spi)
{
struct rtc_device *rtc;
int ret;
spi->mode = SPI_MODE_0;
spi->bits_per_word = 8;
ret = spi_setup(spi);
if (ret) {
dev_err(&spi->dev, "Unable to setup SPI\n");
return ret;
}
/* Start the oscillator but don't set the value of EXTOSC bit */
mcp795_start_oscillator(&spi->dev, NULL);
/* Clear the 12 hour mode flag*/
mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
&mcp795_rtc_ops, THIS_MODULE);
if (IS_ERR(rtc))
return PTR_ERR(rtc);
spi_set_drvdata(spi, rtc);
return 0;
}
#ifdef CONFIG_OF
static const struct of_device_id mcp795_of_match[] = {
{ .compatible = "maxim,mcp795" },
{ }
};
MODULE_DEVICE_TABLE(of, mcp795_of_match);
#endif
static struct spi_driver mcp795_driver = {
.driver = {
.name = "rtc-mcp795",
.of_match_table = of_match_ptr(mcp795_of_match),
},
.probe = mcp795_probe,
};
module_spi_driver(mcp795_driver);
MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:mcp795");
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