diff options
Diffstat (limited to 'drivers/rtc/rtc-dm355evm.c')
| -rw-r--r-- | drivers/rtc/rtc-dm355evm.c | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-dm355evm.c b/drivers/rtc/rtc-dm355evm.c new file mode 100644 index 00000000000..58d4e18530d --- /dev/null +++ b/drivers/rtc/rtc-dm355evm.c @@ -0,0 +1,175 @@ +/* + * rtc-dm355evm.c - access battery-backed counter in MSP430 firmware + * + * Copyright (c) 2008 by David Brownell + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + */ +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/rtc.h> +#include <linux/platform_device.h> + +#include <linux/i2c/dm355evm_msp.h> + + +/* + * The MSP430 firmware on the DM355 EVM uses a watch crystal to feed + * a 1 Hz counter. When a backup battery is supplied, that makes a + * reasonable RTC for applications where alarms and non-NTP drift + * compensation aren't important. + * + * The only real glitch is the inability to read or write all four + * counter bytes atomically: the count may increment in the middle + * of an operation, causing trouble when the LSB rolls over. + * + * This driver was tested with firmware revision A4. + */ +union evm_time { + u8 bytes[4]; + u32 value; +}; + +static int dm355evm_rtc_read_time(struct device *dev, struct rtc_time *tm) +{ + union evm_time time; + int status; + int tries = 0; + + do { + /* + * Read LSB(0) to MSB(3) bytes. Defend against the counter + * rolling over by re-reading until the value is stable, + * and assuming the four reads take at most a few seconds. + */ + status = dm355evm_msp_read(DM355EVM_MSP_RTC_0); + if (status < 0) + return status; + if (tries && time.bytes[0] == status) + break; + time.bytes[0] = status; + + status = dm355evm_msp_read(DM355EVM_MSP_RTC_1); + if (status < 0) + return status; + if (tries && time.bytes[1] == status) + break; + time.bytes[1] = status; + + status = dm355evm_msp_read(DM355EVM_MSP_RTC_2); + if (status < 0) + return status; + if (tries && time.bytes[2] == status) + break; + time.bytes[2] = status; + + status = dm355evm_msp_read(DM355EVM_MSP_RTC_3); + if (status < 0) + return status; + if (tries && time.bytes[3] == status) + break; + time.bytes[3] = status; + + } while (++tries < 5); + + dev_dbg(dev, "read timestamp %08x\n", time.value); + + rtc_time_to_tm(le32_to_cpu(time.value), tm); + return 0; +} + +static int dm355evm_rtc_set_time(struct device *dev, struct rtc_time *tm) +{ + union evm_time time; + unsigned long value; + int status; + + rtc_tm_to_time(tm, &value); + time.value = cpu_to_le32(value); + + dev_dbg(dev, "write timestamp %08x\n", time.value); + + /* + * REVISIT handle non-atomic writes ... maybe just retry until + * byte[1] sticks (no rollover)? + */ + status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0); + if (status < 0) + return status; + + status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1); + if (status < 0) + return status; + + status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2); + if (status < 0) + return status; + + status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3); + if (status < 0) + return status; + + return 0; +} + +static struct rtc_class_ops dm355evm_rtc_ops = { + .read_time = dm355evm_rtc_read_time, + .set_time = dm355evm_rtc_set_time, +}; + +/*----------------------------------------------------------------------*/ + +static int __devinit dm355evm_rtc_probe(struct platform_device *pdev) +{ + struct rtc_device *rtc; + + rtc = rtc_device_register(pdev->name, + &pdev->dev, &dm355evm_rtc_ops, THIS_MODULE); + if (IS_ERR(rtc)) { + dev_err(&pdev->dev, "can't register RTC device, err %ld\n", + PTR_ERR(rtc)); + return PTR_ERR(rtc); + } + platform_set_drvdata(pdev, rtc); + + return 0; +} + +static int __devexit dm355evm_rtc_remove(struct platform_device *pdev) +{ + struct rtc_device *rtc = platform_get_drvdata(pdev); + + rtc_device_unregister(rtc); + platform_set_drvdata(pdev, NULL); + return 0; +} + +/* + * I2C is used to talk to the MSP430, but this platform device is + * exposed by an MFD driver that manages I2C communications. + */ +static struct platform_driver rtc_dm355evm_driver = { + .probe = dm355evm_rtc_probe, + .remove = __devexit_p(dm355evm_rtc_remove), + .driver = { + .owner = THIS_MODULE, + .name = "rtc-dm355evm", + }, +}; + +static int __init dm355evm_rtc_init(void) +{ + return platform_driver_register(&rtc_dm355evm_driver); +} +module_init(dm355evm_rtc_init); + +static void __exit dm355evm_rtc_exit(void) +{ + platform_driver_unregister(&rtc_dm355evm_driver); +} +module_exit(dm355evm_rtc_exit); + +MODULE_LICENSE("GPL"); |