[linux.git] / drivers / rtc / rtc-dm355evm.c

/*
 * 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/mfd/dm355evm_msp.h>
#include <linux/module.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 const struct rtc_class_ops dm355evm_rtc_ops = {
	.read_time	= dm355evm_rtc_read_time,
	.set_time	= dm355evm_rtc_set_time,
};

/*----------------------------------------------------------------------*/

static int dm355evm_rtc_probe(struct platform_device *pdev)
{
	struct rtc_device *rtc;

	rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
					&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;
}

/*
 * 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,
	.driver		= {
		.name	= "rtc-dm355evm",
	},
};

module_platform_driver(rtc_dm355evm_driver);

MODULE_LICENSE("GPL");
Commit	Line	Data
afd8d0f9 DB	1	/*
	2	* rtc-dm355evm.c - access battery-backed counter in MSP430 firmware
	3	*
	4	* Copyright (c) 2008 by David Brownell
	5	*
	6	* This program is free software; you can redistribute it and/or
	7	* modify it under the terms of the GNU General Public License
	8	* as published by the Free Software Foundation; either version
	9	* 2 of the License, or (at your option) any later version.
	10	*/
	11	#include <linux/kernel.h>
	12	#include <linux/init.h>
	13	#include <linux/rtc.h>
	14	#include <linux/platform_device.h>
	15
0335a955	16	#include <linux/mfd/dm355evm_msp.h>
2113852b	17	#include <linux/module.h>
afd8d0f9 DB	18
	19
	20	/*
	21	* The MSP430 firmware on the DM355 EVM uses a watch crystal to feed
	22	* a 1 Hz counter. When a backup battery is supplied, that makes a
	23	* reasonable RTC for applications where alarms and non-NTP drift
	24	* compensation aren't important.
	25	*
	26	* The only real glitch is the inability to read or write all four
	27	* counter bytes atomically: the count may increment in the middle
	28	* of an operation, causing trouble when the LSB rolls over.
	29	*
	30	* This driver was tested with firmware revision A4.
	31	*/
	32	union evm_time {
	33	u8 bytes[4];
	34	u32 value;
	35	};
	36
	37	static int dm355evm_rtc_read_time(struct device dev, struct rtc_time tm)
	38	{
	39	union evm_time time;
	40	int status;
	41	int tries = 0;
	42
	43	do {
	44	/*
	45	* Read LSB(0) to MSB(3) bytes. Defend against the counter
	46	* rolling over by re-reading until the value is stable,
	47	* and assuming the four reads take at most a few seconds.
	48	*/
	49	status = dm355evm_msp_read(DM355EVM_MSP_RTC_0);
	50	if (status < 0)
	51	return status;
	52	if (tries && time.bytes[0] == status)
	53	break;
	54	time.bytes[0] = status;
	55
	56	status = dm355evm_msp_read(DM355EVM_MSP_RTC_1);
	57	if (status < 0)
	58	return status;
	59	if (tries && time.bytes[1] == status)
	60	break;
	61	time.bytes[1] = status;
	62
	63	status = dm355evm_msp_read(DM355EVM_MSP_RTC_2);
	64	if (status < 0)
	65	return status;
	66	if (tries && time.bytes[2] == status)
	67	break;
	68	time.bytes[2] = status;
	69
	70	status = dm355evm_msp_read(DM355EVM_MSP_RTC_3);
	71	if (status < 0)
	72	return status;
	73	if (tries && time.bytes[3] == status)
	74	break;
	75	time.bytes[3] = status;
	76
	77	} while (++tries < 5);
	78
	79	dev_dbg(dev, "read timestamp %08x\n", time.value);
	80
	81	rtc_time_to_tm(le32_to_cpu(time.value), tm);
82	return 0;
83	}
84
85	static int dm355evm_rtc_set_time(struct device dev, struct rtc_time tm)
86	{
87	union evm_time time;
88	unsigned long value;
89	int status;
90
91	rtc_tm_to_time(tm, &value);
92	time.value = cpu_to_le32(value);
93
94	dev_dbg(dev, "write timestamp %08x\n", time.value);
95
96	/*
97	* REVISIT handle non-atomic writes ... maybe just retry until
98	* byte[1] sticks (no rollover)?
99	*/
100	status = dm355evm_msp_write(time.bytes[0], DM355EVM_MSP_RTC_0);
101	if (status < 0)
102	return status;
103
104	status = dm355evm_msp_write(time.bytes[1], DM355EVM_MSP_RTC_1);
105	if (status < 0)
106	return status;
107
108	status = dm355evm_msp_write(time.bytes[2], DM355EVM_MSP_RTC_2);
109	if (status < 0)
110	return status;
111
112	status = dm355evm_msp_write(time.bytes[3], DM355EVM_MSP_RTC_3);
113	if (status < 0)
114	return status;
115
116	return 0;
117	}
118
8bc57e7f	119	static const struct rtc_class_ops dm355evm_rtc_ops = {
afd8d0f9 DB	120	.read_time = dm355evm_rtc_read_time,
	121	.set_time = dm355evm_rtc_set_time,
	122	};
	123
	124	/----------------------------------------------------------------------/
	125
5a167f45	126	static int dm355evm_rtc_probe(struct platform_device *pdev)
afd8d0f9 DB	127	{
	128	struct rtc_device *rtc;
	129
9f421f8d JH	130	rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
9f421f8d JH	131	&dm355evm_rtc_ops, THIS_MODULE);
afd8d0f9 DB	132	if (IS_ERR(rtc)) {
	133	dev_err(&pdev->dev, "can't register RTC device, err %ld\n",
	134	PTR_ERR(rtc));
	135	return PTR_ERR(rtc);
	136	}
	137	platform_set_drvdata(pdev, rtc);
	138
	139	return 0;
	140	}
	141
afd8d0f9 DB	142	/*
	143	* I2C is used to talk to the MSP430, but this platform device is
	144	* exposed by an MFD driver that manages I2C communications.
	145	*/
	146	static struct platform_driver rtc_dm355evm_driver = {
	147	.probe = dm355evm_rtc_probe,
afd8d0f9	148	.driver = {
afd8d0f9 DB	149	.name = "rtc-dm355evm",
	150	},
	151	};
	152
0c4eae66	153	module_platform_driver(rtc_dm355evm_driver);
afd8d0f9 DB	154
afd8d0f9 DB	155	MODULE_LICENSE("GPL");