i.MX 6ULL 驱动开发 二十：RTC

一、RTC 概述

RTC(real-time clock) 为操作系统中的实时时钟设备，为操作系统提供精准的实时时间和定时报警功能。当设备下电后，通过外置电池供电，RTC 继续记录操作系统时间；设备上电后，RTC 提供实时时钟给操作系统，确保断电后系统时间的连续性。

二、iMX6ULL 的 RTC 原理

三、Linux 内核中 RTC 驱动原理

参考：内核驱动 （三）Linux系统时钟RTC_LouisGou的博客-CSDN博客_linux rtc。

RTC 设备驱动是一个标准的字符设备驱动，应用程序通过 open、 release、 read、 write 和 ioctl 等函数完成对 RTC 设备的操作。

Linux 内核使用 rtc_device 结构体描述 RTC 设备，因此 RTC 设备驱动就是申请并初始化 rtc_device，最后将 rtc_device 注册到 Linux 内核里面。rtc_device 结构体中 rtc_class_ops 结构体描述 RTC 设备底层操作函数。 rtc_class_ops 结构体函数集包括从 RTC 设备中读取时间、向 RTC 设备写入新的时间等。
值等。

struct rtc_device 结构体定义如下：

struct rtc_device
{
	struct device dev;
	struct module *owner;

	int id;
	char name[RTC_DEVICE_NAME_SIZE];

	const struct rtc_class_ops *ops;
	struct mutex ops_lock;

	struct cdev char_dev;
	unsigned long flags;

	unsigned long irq_data;
	spinlock_t irq_lock;
	wait_queue_head_t irq_queue;
	struct fasync_struct *async_queue;

	struct rtc_task *irq_task;
	spinlock_t irq_task_lock;
	int irq_freq;
	int max_user_freq;

	struct timerqueue_head timerqueue;
	struct rtc_timer aie_timer;
	struct rtc_timer uie_rtctimer;
	struct hrtimer pie_timer; /* sub second exp, so needs hrtimer */
	int pie_enabled;
	struct work_struct irqwork;
	/* Some hardware can't support UIE mode */
	int uie_unsupported;

#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
	struct work_struct uie_task;
	struct timer_list uie_timer;
	/* Those fields are protected by rtc->irq_lock */
	unsigned int oldsecs;
	unsigned int uie_irq_active:1;
	unsigned int stop_uie_polling:1;
	unsigned int uie_task_active:1;
	unsigned int uie_timer_active:1;
#endif
};
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• dev：设备；
• id：ID；
• name：名字；
• ops：RTC 设备底层操作函数；
• char_dev：字符设备；

struct rtc_class_ops 结构体定义如下：

/*
 * For these RTC methods the device parameter is the physical device
 * on whatever bus holds the hardware (I2C, Platform, SPI, etc), which
 * was passed to rtc_device_register().  Its driver_data normally holds
 * device state, including the rtc_device pointer for the RTC.
 *
 * Most of these methods are called with rtc_device.ops_lock held,
 * through the rtc_*(struct rtc_device *, ...) calls.
 *
 * The (current) exceptions are mostly filesystem hooks:
 *   - the proc() hook for procfs
 *   - non-ioctl() chardev hooks:  open(), release(), read_callback()
 *
 * REVISIT those periodic irq calls *do* have ops_lock when they're
 * issued through ioctl() ...
 */
struct rtc_class_ops {
	int (*open)(struct device *);
	void (*release)(struct device *);
	int (*ioctl)(struct device *, unsigned int, unsigned long);
	int (*read_time)(struct device *, struct rtc_time *);
	int (*set_time)(struct device *, struct rtc_time *);
	int (*read_alarm)(struct device *, struct rtc_wkalrm *);
	int (*set_alarm)(struct device *, struct rtc_wkalrm *);
	int (*proc)(struct device *, struct seq_file *);
	int (*set_mmss64)(struct device *, time64_t secs);
	int (*set_mmss)(struct device *, unsigned long secs);
	int (*read_callback)(struct device *, int data);
	int (*alarm_irq_enable)(struct device *, unsigned int enabled);
};
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注意：struct rtc_device 结构体和 struct rtc_class_ops 结构体定义在 include/linux/rtc.h。

Linux 内核提供了一个 RTC 通用字符设备驱动文件，定义在 drivers/rtc/rtc-dev.c 文件中， rtc-dev.c 文件提供了所有 RTC 设备向应用层提供的 file_operations 函数操作集，如下所示：

static const struct file_operations rtc_dev_fops = {
	.owner		= THIS_MODULE,
	.llseek		= no_llseek,
	.read		= rtc_dev_read,
	.poll		= rtc_dev_poll,
	.unlocked_ioctl	= rtc_dev_ioctl,
	.open		= rtc_dev_open,
	.release	= rtc_dev_release,
	.fasync		= rtc_dev_fasync,
};
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四、Linux 中 RTC 驱动分析

file_operations、rtc_device 和 rtc_class_ops 结构体建立联系过程如下：

1、通过设备树确定驱动源码，设备树内容如下：

snvs_rtc: snvs-rtc-lp {
	compatible = "fsl,sec-v4.0-mon-rtc-lp";
	regmap = <&snvs>;
	offset = <0x34>;
	interrupts = <GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 20 IRQ_TYPE_LEVEL_HIGH>;
};
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通过 fsl,sec-v4.0-mon-rtc-lp 字符串确定驱动相关源码。

2、驱动源码确定

static const struct of_device_id snvs_dt_ids[] = {
	{ .compatible = "fsl,sec-v4.0-mon-rtc-lp", },
	{ /* sentinel */ }
};
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驱动源码路径：linux\drivers\rtc\rtc-snvs.c。

3、驱动源码分析

static struct platform_driver snvs_rtc_driver = {
	.driver = {
		.name	= "snvs_rtc",
		.pm	= SNVS_RTC_PM_OPS,
		.of_match_table = snvs_dt_ids,
	},
	.probe		= snvs_rtc_probe,
};
module_platform_driver(snvs_rtc_driver);
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通过以上信息，可以确定 RTC 驱动框架为 platform，当设备和驱动匹配成功后，snvs_rtc_probe 函数执行。

4、snvs_rtc_probe 函数分析

struct snvs_rtc_data {
	struct rtc_device *rtc;
	struct regmap *regmap;
	int offset;
	int irq;
	struct clk *clk;
};
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static int snvs_rtc_probe(struct platform_device *pdev)
{
	struct snvs_rtc_data *data;
	struct resource *res;
	int ret;
	void __iomem *mmio;

	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
	if (!data)
		return -ENOMEM;

	data->regmap = syscon_regmap_lookup_by_phandle(pdev->dev.of_node, "regmap");

	if (IS_ERR(data->regmap)) {
		dev_warn(&pdev->dev, "snvs rtc: you use old dts file, please update it\n");
		res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

		mmio = devm_ioremap_resource(&pdev->dev, res);
		if (IS_ERR(mmio))
			return PTR_ERR(mmio);

		data->regmap = devm_regmap_init_mmio(&pdev->dev, mmio, &snvs_rtc_config);
	} else {
		data->offset = SNVS_LPREGISTER_OFFSET;
		of_property_read_u32(pdev->dev.of_node, "offset", &data->offset);
	}

	if (!data->regmap) {
		dev_err(&pdev->dev, "Can't find snvs syscon\n");
		return -ENODEV;
	}

	data->irq = platform_get_irq(pdev, 0);
	if (data->irq < 0)
		return data->irq;

	data->clk = devm_clk_get(&pdev->dev, "snvs-rtc");
	if (IS_ERR(data->clk)) {
		data->clk = NULL;
	} else {
		ret = clk_prepare_enable(data->clk);
		if (ret) {
			dev_err(&pdev->dev,
				"Could not prepare or enable the snvs clock\n");
			return ret;
		}
	}

	platform_set_drvdata(pdev, data);

	/* Initialize glitch detect */
	regmap_write(data->regmap, data->offset + SNVS_LPPGDR, SNVS_LPPGDR_INIT);

	/* Clear interrupt status */
	regmap_write(data->regmap, data->offset + SNVS_LPSR, 0xffffffff);

	/* Enable RTC */
	snvs_rtc_enable(data, true);

	device_init_wakeup(&pdev->dev, true);

	ret = devm_request_irq(&pdev->dev, data->irq, snvs_rtc_irq_handler,
			       IRQF_SHARED, "rtc alarm", &pdev->dev);
	if (ret) {
		dev_err(&pdev->dev, "failed to request irq %d: %d\n",
			data->irq, ret);
		goto error_rtc_device_register;
	}

	data->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
					&snvs_rtc_ops, THIS_MODULE);
	if (IS_ERR(data->rtc)) {
		ret = PTR_ERR(data->rtc);
		dev_err(&pdev->dev, "failed to register rtc: %d\n", ret);
		goto error_rtc_device_register;
	}

	return 0;

error_rtc_device_register:
	if (data->clk)
		clk_disable_unprepare(data->clk);

	return ret;
}
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• 分配并初始化 rtc_device。

• 调用 devm_rtc_device_register 向内核注册 RTC 设备。

• devm_rtc_device_register 中调用 rtc_device_register 完成 RTC 设备注册。

5、rtc_device_register

/**
 * rtc_device_register - register w/ RTC class
 * @dev: the device to register
 *
 * rtc_device_unregister() must be called when the class device is no
 * longer needed.
 *
 * Returns the pointer to the new struct class device.
 */
struct rtc_device *rtc_device_register(const char *name, struct device *dev,
					const struct rtc_class_ops *ops,
					struct module *owner)
{
	struct rtc_device *rtc;
	struct rtc_wkalrm alrm;
	int of_id = -1, id = -1, err;

	if (dev->of_node)
		of_id = of_alias_get_id(dev->of_node, "rtc");
	else if (dev->parent && dev->parent->of_node)
		of_id = of_alias_get_id(dev->parent->of_node, "rtc");

	if (of_id >= 0) {
		id = ida_simple_get(&rtc_ida, of_id, of_id + 1,
				    GFP_KERNEL);
		if (id < 0)
			dev_warn(dev, "/aliases ID %d not available\n",
				    of_id);
	}

	if (id < 0) {
		id = ida_simple_get(&rtc_ida, 0, 0, GFP_KERNEL);
		if (id < 0) {
			err = id;
			goto exit;
		}
	}

	rtc = kzalloc(sizeof(struct rtc_device), GFP_KERNEL);
	if (rtc == NULL) {
		err = -ENOMEM;
		goto exit_ida;
	}

	rtc->id = id;
	rtc->ops = ops;
	rtc->owner = owner;
	rtc->irq_freq = 1;
	rtc->max_user_freq = 64;
	rtc->dev.parent = dev;
	rtc->dev.class = rtc_class;
	rtc->dev.release = rtc_device_release;

	mutex_init(&rtc->ops_lock);
	spin_lock_init(&rtc->irq_lock);
	spin_lock_init(&rtc->irq_task_lock);
	init_waitqueue_head(&rtc->irq_queue);

	/* Init timerqueue */
	timerqueue_init_head(&rtc->timerqueue);
	INIT_WORK(&rtc->irqwork, rtc_timer_do_work);
	/* Init aie timer */
	rtc_timer_init(&rtc->aie_timer, rtc_aie_update_irq, (void *)rtc);
	/* Init uie timer */
	rtc_timer_init(&rtc->uie_rtctimer, rtc_uie_update_irq, (void *)rtc);
	/* Init pie timer */
	hrtimer_init(&rtc->pie_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	rtc->pie_timer.function = rtc_pie_update_irq;
	rtc->pie_enabled = 0;

	strlcpy(rtc->name, name, RTC_DEVICE_NAME_SIZE);
	dev_set_name(&rtc->dev, "rtc%d", id);

	/* Check to see if there is an ALARM already set in hw */
	err = __rtc_read_alarm(rtc, &alrm);

	if (!err && !rtc_valid_tm(&alrm.time))
		rtc_initialize_alarm(rtc, &alrm);

	rtc_dev_prepare(rtc);

	err = device_register(&rtc->dev);
	if (err) {
		put_device(&rtc->dev);
		goto exit_kfree;
	}

	rtc_dev_add_device(rtc);
	rtc_sysfs_add_device(rtc);
	rtc_proc_add_device(rtc);

	dev_info(dev, "rtc core: registered %s as %s\n",
			rtc->name, dev_name(&rtc->dev));

	return rtc;

exit_kfree:
	kfree(rtc);

exit_ida:
	ida_simple_remove(&rtc_ida, id);

exit:
	dev_err(dev, "rtc core: unable to register %s, err = %d\n",
			name, err);
	return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(rtc_device_register);
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• rtc_dev_prepare 函数中调用 cdev_init 完成 rtc_dev_fops（struct file_operations） 操作集注册。
• rtc_dev_add_device 函数中调用 cdev_add 完成字符设备驱动注册。

五、Linux 下 RTC 时间相关操作

1、确定 RTC 是否启动

2、查看 RTC 时间

Linux 内核通过 RTC 为系统提供时钟，通过 date 命令即可查看 Linux 系统时钟：

# date
Thu Jan  1 00:04:34 UTC 1970
#
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3、设置 RTC 时间

# date
Thu Jan  1 00:06:53 UTC 1970
# date -s "2022-11-01 21:44:00"
Tue Nov  1 21:44:00 UTC 2022
# date
Tue Nov  1 21:44:02 UTC 2022
#
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使用 “date -s” 命令仅仅是将当前系统时间设置了，此时间还没有写入到 iMX6ULL 内部 RTC 里面或其他的 RTC 芯片里面，因此系统重启以后时间又会丢失。我们需要将当前的时间写入到 RTC 里面，这里要用到 hwclock 命令，输入如下命令将系统时间写入到 RTC 里面：

hwclock -w # 将当前系统时间写入到 RTC 里面
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4、date 帮助信息

# date -h
date: invalid option -- 'h'
BusyBox v1.35.0 (2022-09-25 01:42:03 PDT) multi-call binary.

Usage: date [OPTIONS] [+FMT] [[-s] TIME]

Display time (using +FMT), or set time

        -u              Work in UTC (don't convert to local time)
        [-s] TIME       Set time to TIME
        -d TIME         Display TIME, not 'now'
        -D FMT          FMT (strptime format) for -s/-d TIME conversion
        -r FILE         Display last modification time of FILE
        -R              Output RFC-2822 date
        -I[SPEC]        Output ISO-8601 date
                        SPEC=date (default), hours, minutes, seconds or ns

Recognized TIME formats:
        @seconds_since_1970
        hh:mm[:ss]
        [YYYY.]MM.DD-hh:mm[:ss]
        YYYY-MM-DD hh:mm[:ss]
        [[[[[YY]YY]MM]DD]hh]mm[.ss]
        'date TIME' form accepts MMDDhhmm[[YY]YY][.ss] instead
#
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5、hwclock 帮助信息

# hwclock -h
hwclock: invalid option -- 'h'
BusyBox v1.35.0 (2022-09-25 01:42:03 PDT) multi-call binary.

Usage: hwclock [-swul] [--systz] [-f DEV]

Show or set hardware clock (RTC)

        -s      Set system time from RTC
        -w      Set RTC from system time
        --systz Set in-kernel timezone, correct system time
                if RTC is kept in local time
        -f DEV  Use specified device (e.g. /dev/rtc2)
        -u      Assume RTC is kept in UTC
        -l      Assume RTC is kept in local time
                (if neither is given, read from /var/lib/hwclock/adjtime)
#
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