Qcom平台RTC驱动分析

相关文件list：

pm8998.dtsi　---RTC dts配置
qpnp-rtc.c　 ---qcom RTC驱动
class.c　　　 ---RTC相关class
interface.c  ---相关RTC功能的接口定义
hctosys.c    ---一开机通过RTC设置系统时间
rtc-dev.c　　 ---RTC device fops接口：open、close、ioctl、poll等

简述：

所谓RTC（Real Time Clock），用于关机时继续计算系统日期和时间。是基于硬件的功能。也可以RTC做Alarm来设置power on/off。

驱动分析：

首先在dts的Document中看到两个配置项：

- qcom,qpnp-rtc-write: This property enables/disables rtc write
                       0 = Disable rtc writes.
                       1 = Enable rtc writes.
- qcom,qpnp-rtc-alarm-pwrup:	This property enables/disables
                                feature of powering up phone (from
                                power down state) through alarm
                                interrupt.
                                If not mentioned rtc driver will
                                disable feature of powring-up
                                phone through alarm.
                                0 = Disable powering up of phone
                                    through alarm interrupt.
                                1 = Enable powering up of phone
                                    through alarm interrupt.            

一个是是否使能写RTC时间的功能。另一个是是否支持RTC alarm开机的功能。

接下来，再看RTC的驱动部分，从qpnp-rtc.c：

其中根据.compatible = "qcom,qpnp-rtc"匹配成功后走到probe，probe中获取了dts中上面两条配置参数，从而进行初始化。获取RTC/Alarm相关的寄存器和资源，并通过操作寄存器enable RTC相关功能。注册了RTC中断并配置了RTC相关操作的api。

通过dts的配置，使用不同的ops，从而实现支持write RTC与否。

//这个是不支持write RTC的ops
static const struct rtc_class_ops qpnp_rtc_ro_ops = {
    .read_time = qpnp_rtc_read_time,
    .set_alarm = qpnp_rtc_set_alarm,
    .read_alarm = qpnp_rtc_read_alarm,
    .alarm_irq_enable = qpnp_rtc_alarm_irq_enable,
};

//这个是支持读写 RTC的ops，就是多了个write的接口
static const struct rtc_class_ops qpnp_rtc_rw_ops = {
    .read_time = qpnp_rtc_read_time,
    .set_alarm = qpnp_rtc_set_alarm,
    .read_alarm = qpnp_rtc_read_alarm,
    .alarm_irq_enable = qpnp_rtc_alarm_irq_enable,
    .set_time = qpnp_rtc_set_time,
};

static int qpnp_rtc_probe(struct platform_device *pdev)
{
    const struct rtc_class_ops *rtc_ops = &qpnp_rtc_ro_ops; //默认使用不支持RTC write的ops
    int rc;
    u8 subtype;
    struct qpnp_rtc *rtc_dd;
    unsigned int base;
    struct device_node *child;

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

    rtc_dd->regmap = dev_get_regmap(pdev->dev.parent, NULL);
    if (!rtc_dd->regmap) {
        dev_err(&pdev->dev, "Couldn't get parent's regmap\n");
        return -EINVAL;
    }

    /* Get the rtc write property */
    rc = of_property_read_u32(pdev->dev.of_node, "qcom,qpnp-rtc-write",
                        &rtc_dd->rtc_write_enable); //读取dts中的RTC write配置
    if (rc && rc != -EINVAL) {
        dev_err(&pdev->dev,
            "Error reading rtc_write_enable property %d\n", rc);
        return rc;
    }

    rc = of_property_read_u32(pdev->dev.of_node,
                        "qcom,qpnp-rtc-alarm-pwrup",
                        &rtc_dd->rtc_alarm_powerup); //读取dts中RTC alarm powerup的配置
    if (rc && rc != -EINVAL) {
        dev_err(&pdev->dev,
            "Error reading rtc_alarm_powerup property %d\n", rc);
        return rc;
    }

    /* Initialise spinlock to protect RTC control register */
    spin_lock_init(&rtc_dd->alarm_ctrl_lock);

    rtc_dd->rtc_dev = &(pdev->dev);
    rtc_dd->pdev = pdev;

    if (of_get_available_child_count(pdev->dev.of_node) == ) {
        pr_err("no child nodes\n");
        rc = -ENXIO;
        goto fail_rtc_enable;
    }

    /* Get RTC/ALARM resources */
    for_each_available_child_of_node(pdev->dev.of_node, child) {
        rc = of_property_read_u32(child, "reg", &base);
        if (rc < ) {
            dev_err(&pdev->dev,
                "Couldn't find reg in node = %s rc = %d\n",
                child->full_name, rc);
            goto fail_rtc_enable;
        }

        rc = qpnp_read_wrapper(rtc_dd, &subtype,
                base + REG_OFFSET_PERP_SUBTYPE, );
        if (rc) {
            dev_err(&pdev->dev,
                "Peripheral subtype read failed\n");
            goto fail_rtc_enable;
        }

        switch (subtype) {
        case RTC_PERPH_SUBTYPE:
            rtc_dd->rtc_base = base;
            break;
        case ALARM_PERPH_SUBTYPE:
            rtc_dd->alarm_base = base;
            rtc_dd->rtc_alarm_irq = of_irq_get(child, );
            if (rtc_dd->rtc_alarm_irq < ) {
                dev_err(&pdev->dev, "ALARM IRQ absent\n");
                rc = -ENXIO;
                goto fail_rtc_enable;
            }
            break;
        default:
            dev_err(&pdev->dev, "Invalid peripheral subtype\n");
            rc = -EINVAL;
            goto fail_rtc_enable;
        }
    }

    rc = qpnp_read_wrapper(rtc_dd, &rtc_dd->rtc_ctrl_reg,
                rtc_dd->rtc_base + REG_OFFSET_RTC_CTRL, );
    if (rc) {
        dev_err(&pdev->dev, "Read from RTC control reg failed\n");
        goto fail_rtc_enable;
    }

    if (!(rtc_dd->rtc_ctrl_reg & BIT_RTC_ENABLE)) {
        dev_err(&pdev->dev, "RTC h/w disabled, rtc not registered\n");
        goto fail_rtc_enable;
    }

    rc = qpnp_read_wrapper(rtc_dd, &rtc_dd->alarm_ctrl_reg1,
                rtc_dd->alarm_base + REG_OFFSET_ALARM_CTRL1, );
    if (rc) {
        dev_err(&pdev->dev, "Read from  Alarm control reg failed\n");
        goto fail_rtc_enable;
    }
    /* Enable abort enable feature */
    rtc_dd->alarm_ctrl_reg1 |= BIT_RTC_ABORT_ENABLE;
    rc = qpnp_write_wrapper(rtc_dd, &rtc_dd->alarm_ctrl_reg1,
            rtc_dd->alarm_base + REG_OFFSET_ALARM_CTRL1, );
    if (rc) {
        dev_err(&pdev->dev, "SPMI write failed!\n");
        goto fail_rtc_enable;
    }

    if (rtc_dd->rtc_write_enable == true) //判断dts中配置如果要支持RTC write功能，那就重新赋值，使用将RTC RW都支持的ops接口
        rtc_ops = &qpnp_rtc_rw_ops;

    dev_set_drvdata(&pdev->dev, rtc_dd);

    /* Register the RTC device */
    rtc_dd->rtc = rtc_device_register("qpnp_rtc", &pdev->dev,
                      rtc_ops, THIS_MODULE);
    if (IS_ERR(rtc_dd->rtc)) {
        dev_err(&pdev->dev, "%s: RTC registration failed (%ld)\n",
                    __func__, PTR_ERR(rtc_dd->rtc));
        rc = PTR_ERR(rtc_dd->rtc);
        goto fail_rtc_enable;
    }

    /* Request the alarm IRQ */
    rc = request_any_context_irq(rtc_dd->rtc_alarm_irq,
                 qpnp_alarm_trigger, IRQF_TRIGGER_RISING,
                 "qpnp_rtc_alarm", rtc_dd);
    if (rc) {
        dev_err(&pdev->dev, "Request IRQ failed (%d)\n", rc);
        goto fail_req_irq;
    }

    device_init_wakeup(&pdev->dev, );
    enable_irq_wake(rtc_dd->rtc_alarm_irq);

    dev_dbg(&pdev->dev, "Probe success !!\n");

    return ;

fail_req_irq:
    rtc_device_unregister(rtc_dd->rtc);
fail_rtc_enable:
    dev_set_drvdata(&pdev->dev, NULL);

    return rc;
}

而在RTC shutdown时，会根据是否要支持RTC alarm开机，进行中断和寄存器的配置。

static void qpnp_rtc_shutdown(struct platform_device *pdev)
{
    u8 value[] = {};
    u8 reg;
    int rc;
    unsigned long irq_flags;
    struct qpnp_rtc *rtc_dd;
    bool rtc_alarm_powerup;

    if (!pdev) {
        pr_err("qpnp-rtc: spmi device not found\n");
        return;
    }
    rtc_dd = dev_get_drvdata(&pdev->dev);
    if (!rtc_dd) {
        pr_err("qpnp-rtc: rtc driver data not found\n");
        return;
    }
    rtc_alarm_powerup = rtc_dd->rtc_alarm_powerup;
    if (!rtc_alarm_powerup && !poweron_alarm) { //根据flag设置是否disbale RTC alarm的中断，以及通过设置reg，控制是否disable RTC alarm
        spin_lock_irqsave(&rtc_dd->alarm_ctrl_lock, irq_flags);
        dev_dbg(&pdev->dev, "Disabling alarm interrupts\n");

        /* Disable RTC alarms */
        reg = rtc_dd->alarm_ctrl_reg1;
        reg &= ~BIT_RTC_ALARM_ENABLE;
        rc = qpnp_write_wrapper(rtc_dd, &reg,
            rtc_dd->alarm_base + REG_OFFSET_ALARM_CTRL1, );
        if (rc) {
            dev_err(rtc_dd->rtc_dev, "SPMI write failed\n");
            goto fail_alarm_disable;
        }

        /* Clear Alarm register */
        rc = qpnp_write_wrapper(rtc_dd, value,
                rtc_dd->alarm_base + REG_OFFSET_ALARM_RW,
                NUM_8_BIT_RTC_REGS);
        if (rc)
            dev_err(rtc_dd->rtc_dev, "SPMI write failed\n");

fail_alarm_disable:
        spin_unlock_irqrestore(&rtc_dd->alarm_ctrl_lock, irq_flags);
    }
}

内核的开机时间首先是从RTC读取的时间作为基准，之后会通过QCOM time daemon进行corection。QCOM time daemon的代码非open source，所以暂不分析。这里我们仅分析RTC的部分。

而RTC的时间，我们知道第一次开机，这里指的是RTC断电后的第一次开机，RTC时间是1970-01-01 00:00:00（初始时间），这个值就是从RTC中读取出来的。而在使用一段时间之后，再重启手机，这时RTC的时间为=初始时间+使用的时间。也就是说，这个时间会随着使用而不断累计，除非RTC掉电，重置为初始时间。RTC也支持将同步后的时间再次写入RTC，用于校准当前的正确日期和时间。

Case 1 开机系统内核时间设置 from RTC

这里主要分析RTC驱动部分的RTC时间读取，并设置内核系统时间。

log：

[    0.897142] qcom,qpnp-rtc c440000.qcom,spmi:qcom,pm8998@:qcom,pm8998_rtc: rtc core: registered qpnp_rtc as rtc0
[    1.808755] hctosys: [ljj]open rtc device (rtc0)
[    1.808819] qcom,qpnp-rtc c440000.qcom,spmi:qcom,pm8998@:qcom,pm8998_rtc: setting system clock to -- :: UTC ()

上面的代码，可以看到kernel log的最前面是距离开机的时间累计（CLOCK_MONOTONIC），后面的则是RTC读取的UTC时间（CLOCK_REALTIME）。可以看到一开机，就会从RTC中读取UTC时间。

对应代码在hcttosys.c中：

static int __init rtc_hctosys(void)
{
    int err = -ENODEV;
    struct rtc_time tm;
    struct timespec64 tv64 = {
        .tv_nsec = NSEC_PER_SEC >> ,
    };
    struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);
        pr_info("[ljj]open rtc device (%s)\n",
            CONFIG_RTC_HCTOSYS_DEVICE);
    if (rtc == NULL) {
        pr_info("unable to open rtc device (%s)\n",
            CONFIG_RTC_HCTOSYS_DEVICE);
        goto err_open;
    }
    //api 调用
    err = rtc_read_time(rtc, &tm);
    if (err) {
        dev_err(rtc->dev.parent,
            "hctosys: unable to read the hardware clock\n");
        goto err_read;

    }

    tv64.tv_sec = rtc_tm_to_time64(&tm);

#if BITS_PER_LONG == 32
    if (tv64.tv_sec > INT_MAX)
        goto err_read;
#endif
    //设置内核系统时间
    err = do_settimeofday64(&tv64);

    dev_info(rtc->dev.parent,
        "setting system clock to "
        "%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n",
        tm.tm_year + , tm.tm_mon + , tm.tm_mday,
        tm.tm_hour, tm.tm_min, tm.tm_sec,
        (long long) tv64.tv_sec);

err_read:
    rtc_class_close(rtc);

err_open:
    rtc_hctosys_ret = err;

    return err;
}

late_initcall(rtc_hctosys);

int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
{
    int err;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    err = __rtc_read_time(rtc, tm); //调用内部__rtc_read_time
    mutex_unlock(&rtc->ops_lock);
    return err;
}
EXPORT_SYMBOL_GPL(rtc_read_time);
static int __rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
{
    int err;
    if (!rtc->ops)
        err = -ENODEV;
    else if (!rtc->ops->read_time)
        err = -EINVAL;
    else {
        memset(tm, , sizeof(struct rtc_time));
        err = rtc->ops->read_time(rtc->dev.parent, tm); //调用了qpnp-rtc.c中的read_time ops，最后就是通过读取寄存器，来获取RTC硬件计算的时间，具体代码就不贴了
        if (err < ) {
            dev_dbg(&rtc->dev, "read_time: fail to read: %d\n",
                err);
            return err;
        }

        err = rtc_valid_tm(tm);
        if (err < )
            dev_dbg(&rtc->dev, "read_time: rtc_time isn't valid\n");
    }
    return err;
}

Case 2 kernel RTC时间与system时间进行同步

实际是因为RTC中的时间并不一定准，所以会用android system中的时间与RTC时间进行对比同步和更新。也就是上面可能会牵扯到QCOM time Daemon的部分，所以避开这块闭源代码。可以参考如下链接，了解开源代码中内核时间与system时间同步。

kernel log中时间同步的流程，参考自：http://blog.chinaunix.net/uid-23141914-id-5715368.html

Case 3 更新并设置RTC时间

当时间与网络、或者setting同步后，可能需要将当前正确的时间再写入RTC中，以保证RTC中的时间准确。这块我们往上看多一点，从jni开始分析。如下：

路径：frameworks/base/services/core/jni/com_android_server_AlarmManagerService.cpp

static const JNINativeMethod sMethods[] = {
     /* name, signature, funcPtr */
    {"init", "()J", (void*)android_server_AlarmManagerService_init},
    {"close", "(J)V", (void*)android_server_AlarmManagerService_close},
    {"set", "(JIJJ)I", (void*)android_server_AlarmManagerService_set},
    {"waitForAlarm", "(J)I", (void*)android_server_AlarmManagerService_waitForAlarm},
    {"setKernelTime", "(JJ)I", (void*)android_server_AlarmManagerService_setKernelTime}, //设置时间的JNI
    {"setKernelTimezone", "(JI)I", (void*)android_server_AlarmManagerService_setKernelTimezone},
};

static jint android_server_AlarmManagerService_setKernelTime(JNIEnv*, jobject, jlong nativeData, jlong millis)
{
    AlarmImpl *impl = reinterpret_cast<AlarmImpl *>(nativeData);
    struct timeval tv;
    int ret;

    if (millis <=  || millis / 1000LL >= INT_MAX) {
        return -;
    }

    tv.tv_sec = (time_t) (millis / 1000LL);
    tv.tv_usec = (suseconds_t) ((millis % 1000LL) * 1000LL);

    ALOGD("Setting time of day to sec=%d\n", (int) tv.tv_sec);

    ret = impl->setTime(&tv); //调用setTime

    if(ret < ) {
        ALOGW("Unable to set rtc to %ld: %s\n", tv.tv_sec, strerror(errno));
        ret = -;
    }
    return ret;
}

int AlarmImpl::setTime(struct timeval *tv)
{
    struct rtc_time rtc;
    struct tm tm, *gmtime_res;
    int fd;
    int res;

    res = settimeofday(tv, NULL);
    if (res < ) {
        ALOGV("settimeofday() failed: %s\n", strerror(errno));
        return -;
    }

    if (rtc_id < ) {
        ALOGV("Not setting RTC because wall clock RTC was not found");
        errno = ENODEV;
        return -;
    }

    android::String8 rtc_dev = String8::format("/dev/rtc%d", rtc_id);
    fd = open(rtc_dev.string(), O_RDWR); //打开了RTC设备
    if (fd < ) {
        ALOGV("Unable to open %s: %s\n", rtc_dev.string(), strerror(errno));
        return res;
    }

    gmtime_res = gmtime_r(&tv->tv_sec, &tm);
    if (!gmtime_res) {
        ALOGV("gmtime_r() failed: %s\n", strerror(errno));
        res = -;
        goto done;
    }

    memset(&rtc, , sizeof(rtc));
    rtc.tm_sec = tm.tm_sec;
    rtc.tm_min = tm.tm_min;
    rtc.tm_hour = tm.tm_hour;
    rtc.tm_mday = tm.tm_mday;
    rtc.tm_mon = tm.tm_mon;
    rtc.tm_year = tm.tm_year;
    rtc.tm_wday = tm.tm_wday;
    rtc.tm_yday = tm.tm_yday;
    rtc.tm_isdst = tm.tm_isdst;
    res = ioctl(fd, RTC_SET_TIME, &rtc); //通过ioctl设置RTC时间
    if (res < )
        ALOGV("RTC_SET_TIME ioctl failed: %s\n", strerror(errno));
done:
    close(fd);
    return res;
}

接下来就是驱动部分，rtc-dev.c文件中的ioctl接口，最后会调用至qpnp-rtc.c中的set接口，从而将准确的时间写入对应寄存器：

static long rtc_dev_ioctl(struct file *file,
        unsigned int cmd, unsigned long arg)
{
    int err = ;
    struct rtc_device *rtc = file->private_data;
    const struct rtc_class_ops *ops = rtc->ops;
    struct rtc_time tm;
    struct rtc_wkalrm alarm;
    void __user *uarg = (void __user *) arg;

    err = mutex_lock_interruptible(&rtc->ops_lock);
    if (err)
        return err;

    /* check that the calling task has appropriate permissions
     * for certain ioctls. doing this check here is useful
     * to avoid duplicate code in each driver.
     */
    switch (cmd) {
    case RTC_EPOCH_SET:
    case RTC_SET_TIME:
        if (!capable(CAP_SYS_TIME)) //如上面注释所说，设置时间的api必须要有CAP_SYS_TIME的权限
            err = -EACCES;
        break;

    case RTC_IRQP_SET:
        if (arg > rtc->max_user_freq && !capable(CAP_SYS_RESOURCE))
            err = -EACCES;
        break;

    case RTC_PIE_ON:
        if (rtc->irq_freq > rtc->max_user_freq &&
                !capable(CAP_SYS_RESOURCE))
            err = -EACCES;
        break;
    }

    if (err)
        goto done;

    /*
     * Drivers *SHOULD NOT* provide ioctl implementations
     * for these requests.  Instead, provide methods to
     * support the following code, so that the RTC's main
     * features are accessible without using ioctls.
     *
     * RTC and alarm times will be in UTC, by preference,
     * but dual-booting with MS-Windows implies RTCs must
     * use the local wall clock time.
     */

    switch (cmd) {
    case RTC_ALM_READ:
        mutex_unlock(&rtc->ops_lock);

        err = rtc_read_alarm(rtc, &alarm);
        if (err < )
            return err;

        if (copy_to_user(uarg, &alarm.time, sizeof(tm)))
            err = -EFAULT;
        return err;

    case RTC_ALM_SET:
        mutex_unlock(&rtc->ops_lock);

        if (copy_from_user(&alarm.time, uarg, sizeof(tm)))
            return -EFAULT;

        alarm.enabled = ;
        alarm.pending = ;
        alarm.time.tm_wday = -;
        alarm.time.tm_yday = -;
        alarm.time.tm_isdst = -;

        /* RTC_ALM_SET alarms may be up to 24 hours in the future.
         * Rather than expecting every RTC to implement "don't care"
         * for day/month/year fields, just force the alarm to have
         * the right values for those fields.
         *
         * RTC_WKALM_SET should be used instead.  Not only does it
         * eliminate the need for a separate RTC_AIE_ON call, it
         * doesn't have the "alarm 23:59:59 in the future" race.
         *
         * NOTE:  some legacy code may have used invalid fields as
         * wildcards, exposing hardware "periodic alarm" capabilities.
         * Not supported here.
         */
        {
            time64_t now, then;

            err = rtc_read_time(rtc, &tm);
            if (err < )
                return err;
            now = rtc_tm_to_time64(&tm);

            alarm.time.tm_mday = tm.tm_mday;
            alarm.time.tm_mon = tm.tm_mon;
            alarm.time.tm_year = tm.tm_year;
            err  = rtc_valid_tm(&alarm.time);
            if (err < )
                return err;
            then = rtc_tm_to_time64(&alarm.time);

            /* alarm may need to wrap into tomorrow */
            if (then < now) {
                rtc_time64_to_tm(now +  *  * , &tm);
                alarm.time.tm_mday = tm.tm_mday;
                alarm.time.tm_mon = tm.tm_mon;
                alarm.time.tm_year = tm.tm_year;
            }
        }

        return rtc_set_alarm(rtc, &alarm);

    case RTC_RD_TIME:
        mutex_unlock(&rtc->ops_lock);

        err = rtc_read_time(rtc, &tm);
        if (err < )
            return err;

        if (copy_to_user(uarg, &tm, sizeof(tm)))
            err = -EFAULT;
        return err;

    case RTC_SET_TIME:
        mutex_unlock(&rtc->ops_lock);

        if (copy_from_user(&tm, uarg, sizeof(tm))) //获取上层传下来的tm结构
            return -EFAULT;

        return rtc_set_time(rtc, &tm); //通过interface.c的接口，从而调用qpnp-rtc.c的设置RTC寄存器函数，完成RTC时间写入。

    case RTC_PIE_ON:
        err = rtc_irq_set_state(rtc, NULL, );
        break;

    case RTC_PIE_OFF:
        err = rtc_irq_set_state(rtc, NULL, );
        break;

    case RTC_AIE_ON:
        mutex_unlock(&rtc->ops_lock);
        return rtc_alarm_irq_enable(rtc, );

    case RTC_AIE_OFF:
        mutex_unlock(&rtc->ops_lock);
        return rtc_alarm_irq_enable(rtc, );

    case RTC_UIE_ON:
        mutex_unlock(&rtc->ops_lock);
        return rtc_update_irq_enable(rtc, );

    case RTC_UIE_OFF:
        mutex_unlock(&rtc->ops_lock);
        return rtc_update_irq_enable(rtc, );

    case RTC_IRQP_SET:
        err = rtc_irq_set_freq(rtc, NULL, arg);
        break;

    case RTC_IRQP_READ:
        err = put_user(rtc->irq_freq, (unsigned long __user *)uarg);
        break;

    case RTC_WKALM_SET:
        mutex_unlock(&rtc->ops_lock);
        if (copy_from_user(&alarm, uarg, sizeof(alarm)))
            return -EFAULT;

        return rtc_set_alarm(rtc, &alarm);

    case RTC_WKALM_RD:
        mutex_unlock(&rtc->ops_lock);
        err = rtc_read_alarm(rtc, &alarm);
        if (err < )
            return err;

        if (copy_to_user(uarg, &alarm, sizeof(alarm)))
            err = -EFAULT;
        return err;

    default:
        /* Finally try the driver's ioctl interface */
        if (ops->ioctl) {
            err = ops->ioctl(rtc->dev.parent, cmd, arg);
            if (err == -ENOIOCTLCMD)
                err = -ENOTTY;
        } else
            err = -ENOTTY;
        break;
    }

done:
    mutex_unlock(&rtc->ops_lock);
    return err;
}