12.3.3 RTC设备驱动
RTC（实时时钟）借助电池供电，在系统掉电的情况下正常计时。RTC通常还具有产生周期性中断以及闹钟（Alarm）中断的能力，是一种典型的字符设备。作为一种字符设备驱动，RTC需要有file_operations中接口函数的实现，如open（）、release（）、read（）、poll（）、ioctl（）等，而典型的IOCTL包括RTC_SET_TIME、RTC_ALM_READ、RTC_ALM_SET等，这些对于所有的RTC是通用的，只有底层的具体实现与设备相关。
因此，drivers/rtc/rtc-dev.c实现了RTC驱动通用的字符设备驱动层，它实现了file_opearations的成员函数
以及一些通用的关于RTC的控制代码，并向底层导出rtc_device_register（）、rtc_device_unregister（）以注
册和注销RTC（drivers/rtc/class.c）；导出rtc_class_ops结构体以描述底层的RTC硬件操作。
linux/rtc.h
extern struct rtc_device *rtc_device_register(const char *name,
struct device *dev,
const struct rtc_class_ops *ops,
struct module *owner);
extern void rtc_device_unregister(struct rtc_device *rtc);
RTC通用层实现的结果是，底层的RTC驱动不再关心RTC作为字符设备驱动的具体实现，也无需关心一些通用的RTC控制逻辑，如图12.7：
图12.7 Linux RTC设备驱动的分层
例如：drivers/rtc/rtc-s3c.c实现S3C6410的RTC驱动，其注册RTC以及绑定rtc_class_ops的代码如代码清单12.14所示。
static const struct rtc_class_ops s3c_rtcops = {
.open = s3c_rtc_open,
.release = s3c_rtc_release,
.read_time = s3c_rtc_gettime,
.set_time = s3c_rtc_settime,
.read_alarm = s3c_rtc_getalarm,
.set_alarm = s3c_rtc_setalarm,
.proc = s3c_rtc_proc,
.alarm_irq_enable = s3c_rtc_setaie,
};
static int __devinit s3c_rtc_probe(struct platform_device *pdev)
{
struct rtc_device *rtc;
struct rtc_time rtc_tm;
struct resource *res;
int ret;
pr_debug("%s: probe=%p\n", __func__, pdev);
/* find the IRQs */
s3c_rtc_tickno = platform_get_irq(pdev, 1);
if (s3c_rtc_tickno < 0) {
dev_err(&pdev->dev, "no irq for rtc tick\n");
return -ENOENT;
}
s3c_rtc_alarmno = platform_get_irq(pdev, 0);
if (s3c_rtc_alarmno < 0) {
dev_err(&pdev->dev, "no irq for alarm\n");
return -ENOENT;
}
pr_debug("s3c2410_rtc: tick irq %d, alarm irq %d\n",
s3c_rtc_tickno, s3c_rtc_alarmno);
/* get the memory region */
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (res == NULL) {
dev_err(&pdev->dev, "failed to get memory region resource\n");
return -ENOENT;
}
s3c_rtc_mem = request_mem_region(res->start,
res->end-res->start+1,
pdev->name);
if (s3c_rtc_mem == NULL) {
dev_err(&pdev->dev, "failed to reserve memory region\n");
ret = -ENOENT;
goto err_nores;
}
s3c_rtc_base = ioremap(res->start, res->end - res->start + 1);
if (s3c_rtc_base == NULL) {
dev_err(&pdev->dev, "failed ioremap()\n");
ret = -EINVAL;
goto err_nomap;
}
rtc_clk = clk_get(&pdev->dev, "rtc");
if (IS_ERR(rtc_clk)) {
dev_err(&pdev->dev, "failed to find rtc clock source\n");
ret = PTR_ERR(rtc_clk);
rtc_clk = NULL;
goto err_clk;
}
clk_enable(rtc_clk);
/* check to see if everything is setup correctly */
s3c_rtc_enable(pdev, 1);
pr_debug("s3c2410_rtc: RTCCON=%02x\n",
readw(s3c_rtc_base + S3C2410_RTCCON));
device_init_wakeup(&pdev->dev, 1);
/* register RTC and exit */
rtc = rtc_device_register("s3c", &pdev->dev, &s3c_rtcops,
THIS_MODULE);//注册RTC以及绑定rtc_class_ops
if (IS_ERR(rtc)) {
dev_err(&pdev->dev, "cannot attach rtc\n");
ret = PTR_ERR(rtc);
goto err_nortc;
}
s3c_rtc_cpu_type = platform_get_device_id(pdev)->driver_data;
/* Check RTC Time */
s3c_rtc_gettime(NULL, &rtc_tm);
if (rtc_valid_tm(&rtc_tm)) {
rtc_tm.tm_year = 100;
rtc_tm.tm_mon = 0;
rtc_tm.tm_mday = 1;
rtc_tm.tm_hour = 0;
rtc_tm.tm_min = 0;
rtc_tm.tm_sec = 0;
s3c_rtc_settime(NULL, &rtc_tm);
dev_warn(&pdev->dev, "warning: invalid RTC value so initializing it\n");
}
if (s3c_rtc_cpu_type == TYPE_S3C64XX)
rtc->max_user_freq = 32768;
else
rtc->max_user_freq = 128;
platform_set_drvdata(pdev, rtc);
s3c_rtc_setfreq(&pdev->dev, 1);
return 0;
err_nortc:
s3c_rtc_enable(pdev, 0);
clk_disable(rtc_clk);
clk_put(rtc_clk);
err_clk:
iounmap(s3c_rtc_base);
err_nomap:
release_resource(s3c_rtc_mem);
err_nores:
return ret;
}
drivers/rtc/rtc-dev.c以及其调用的drivers/rtc/interface.c等RTC核心层相当于把file_operations中的open（）、release（）、读取和设置时间等都间接“转发”给了底层的实例。
代码清单12.15 RTC核心层“转发”到底层RTC驱动callback（回调）
1、drivers/rtc/rtc-dev.c
static int rtc_dev_open(struct inode *inode, struct file *file)
{
int err;
struct rtc_device *rtc = container_of(inode->i_cdev,
struct rtc_device, char_dev);
const struct rtc_class_ops *ops = rtc->ops;
if (test_and_set_bit_lock(RTC_DEV_BUSY, &rtc->flags))
return -EBUSY;
file->private_data = rtc;
err = ops->open ? ops->open(rtc->dev.parent) : 0;
if (err == 0) {
spin_lock_irq(&rtc->irq_lock);
rtc->irq_data = 0;
spin_unlock_irq(&rtc->irq_lock);
return 0;
}
/* something has gone wrong */
clear_bit_unlock(RTC_DEV_BUSY, &rtc->flags);
return err;
}
2、drivers/rtc/interface.c
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, 0, sizeof(struct rtc_time));
err = rtc->ops->read_time(rtc->dev.parent, tm);
}
return err;
}
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);
mutex_unlock(&rtc->ops_lock);
return err;
}
EXPORT_SYMBOL_GPL(rtc_read_time);
int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
{
int err;
err = rtc_valid_tm(tm);
if (err != 0)
return err;
err = mutex_lock_interruptible(&rtc->ops_lock);
if (err)
return err;
if (!rtc->ops)
err = -ENODEV;
else if (rtc->ops->set_time)
err = rtc->ops->set_time(rtc->dev.parent, tm);
else if (rtc->ops->set_mmss) {
unsigned long secs;
err = rtc_tm_to_time(tm, &secs);
if (err == 0)
err = rtc->ops->set_mmss(rtc->dev.parent, secs);
} else
err = -EINVAL;
mutex_unlock(&rtc->ops_lock);
return err;
}
EXPORT_SYMBOL_GPL(rtc_set_time);
3、drivers/rtc/rtc-dev.c
static long rtc_dev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
int err = 0;
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))
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 < 0)
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 = 0;
alarm.pending = 0;
alarm.time.tm_wday = -1;
alarm.time.tm_yday = -1;
alarm.time.tm_isdst = -1;
/* 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.
*/
{
unsigned long now, then;
err = rtc_read_time(rtc, &tm);
if (err < 0)
return err;
rtc_tm_to_time(&tm, &now);
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 < 0)
return err;
rtc_tm_to_time(&alarm.time, &then);
/* alarm may need to wrap into tomorrow */
if (then < now) {
rtc_time_to_tm(now + 24 * 60 * 60, &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 < 0)
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)))
return -EFAULT;
return rtc_set_time(rtc, &tm);
case RTC_PIE_ON:
err = rtc_irq_set_state(rtc, NULL, 1);
break;
case RTC_PIE_OFF:
err = rtc_irq_set_state(rtc, NULL, 0);
break;
case RTC_AIE_ON:
mutex_unlock(&rtc->ops_lock);
return rtc_alarm_irq_enable(rtc, 1);
case RTC_AIE_OFF:
mutex_unlock(&rtc->ops_lock);
return rtc_alarm_irq_enable(rtc, 0);
case RTC_UIE_ON:
mutex_unlock(&rtc->ops_lock);
return rtc_update_irq_enable(rtc, 1);
case RTC_UIE_OFF:
mutex_unlock(&rtc->ops_lock);
return rtc_update_irq_enable(rtc, 0);
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;
#if 0
case RTC_EPOCH_SET:
#ifndef rtc_epoch
/*
* There were no RTC clocks before 1900.
*/
if (arg < 1900) {
err = -EINVAL;
break;
}
rtc_epoch = arg;
err = 0;
#endif
break;
case RTC_EPOCH_READ:
err = put_user(rtc_epoch, (unsigned long __user *)uarg);
break;
#endif
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 < 0)
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;
}