/* * SPI Driver for Microchip MCP795 RTC * * Copyright (C) Josef Gajdusek * * 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 #include #include #include #include #include #include #include #include /* 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 "); MODULE_LICENSE("GPL"); MODULE_ALIAS("spi:mcp795");