156 lines
3.8 KiB
C
156 lines
3.8 KiB
C
/*
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* rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
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*
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* Copyright (c) 2008 by David Brownell
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/rtc.h>
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#include <linux/platform_device.h>
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#include <linux/i2c/dm355evm_msp.h>
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#include <linux/module.h>
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/*
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* The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
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* a 1 Hz counter. When a backup battery is supplied, that makes a
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* reasonable RTC for applications where alarms and non-NTP drift
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* compensation aren't important.
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*
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* The only real glitch is the inability to read or write all four
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* counter bytes atomically: the count may increment in the middle
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* of an operation, causing trouble when the LSB rolls over.
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*
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* This driver was tested with firmware revision A4.
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*/
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union evm_time {
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u8 bytes[4];
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u32 value;
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};
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static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm)
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{
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union evm_time time;
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int status;
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int tries = 0;
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do {
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/*
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* Read LSB(0) to MSB(3) bytes. Defend against the counter
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* rolling over by re-reading until the value is stable,
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* and assuming the four reads take at most a few seconds.
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*/
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status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
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if (status < 0)
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return status;
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if (tries && time.bytes[0] == status)
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break;
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time.bytes[0] = status;
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status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
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if (status < 0)
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return status;
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if (tries && time.bytes[1] == status)
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break;
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time.bytes[1] = status;
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status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
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if (status < 0)
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return status;
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if (tries && time.bytes[2] == status)
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break;
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time.bytes[2] = status;
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status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
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if (status < 0)
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return status;
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if (tries && time.bytes[3] == status)
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break;
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time.bytes[3] = status;
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} while (++tries < 5);
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dev_dbg(dev, "read timestamp %08x\n", time.value);
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rtc_time_to_tm(le32_to_cpu(time.value), tm);
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return 0;
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}
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static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm)
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{
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union evm_time time;
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unsigned long value;
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int status;
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rtc_tm_to_time(tm, &value);
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time.value = cpu_to_le32(value);
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dev_dbg(dev, "write timestamp %08x\n", time.value);
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/*
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* REVISIT handle non-atomic writes ... maybe just retry until
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* byte[1] sticks (no rollover)?
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*/
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status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
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if (status < 0)
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return status;
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status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
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if (status < 0)
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return status;
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status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
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if (status < 0)
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return status;
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status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
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if (status < 0)
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return status;
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return 0;
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}
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static const struct rtc_class_ops dm355evm_rtc_ops = {
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.read_time = dm355evm_rtc_read_time,
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.set_time = dm355evm_rtc_set_time,
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};
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/*----------------------------------------------------------------------*/
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static int dm355evm_rtc_probe(struct platform_device *pdev)
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{
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struct rtc_device *rtc;
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rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
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&dm355evm_rtc_ops, THIS_MODULE);
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if (IS_ERR(rtc)) {
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dev_err(&pdev->dev, "can't register RTC device, err %ld\n",
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PTR_ERR(rtc));
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return PTR_ERR(rtc);
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}
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platform_set_drvdata(pdev, rtc);
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return 0;
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}
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/*
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* I2C is used to talk to the MSP430, but this platform device is
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* exposed by an MFD driver that manages I2C communications.
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*/
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static struct platform_driver rtc_dm355evm_driver = {
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.probe = dm355evm_rtc_probe,
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.driver = {
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.name = "rtc-dm355evm",
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},
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};
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module_platform_driver(rtc_dm355evm_driver);
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MODULE_LICENSE("GPL");
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