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151 lines
3.5 KiB
151 lines
3.5 KiB
// SPDX-License-Identifier: GPL-2.0+ |
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/* |
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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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#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/mfd/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_time64_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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value = rtc_tm_to_time64(tm); |
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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_allocate_device(&pdev->dev); |
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if (IS_ERR(rtc)) |
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return PTR_ERR(rtc); |
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platform_set_drvdata(pdev, rtc); |
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rtc->ops = &dm355evm_rtc_ops; |
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rtc->range_max = U32_MAX; |
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return devm_rtc_register_device(rtc); |
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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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