Linux内核启动过程分析（十）-----RTC驱动分析

参考https://blog.csdn.net/xuao20060793/article/details/46433263这篇博文
RTC驱动分析：

Class.c (drivers\rtc):subsys_initcall(rtc_init);

static int __init rtc_init(void)
{
	rtc_class = class_create(THIS_MODULE, "rtc");//创建rtc类
	if (IS_ERR(rtc_class)) {
		printk(KERN_ERR "%s: couldn't create class\n", __FILE__);
		return PTR_ERR(rtc_class);
	}
	rtc_class->suspend = rtc_suspend;
	rtc_class->resume = rtc_resume;
	rtc_dev_init();//创建rtc字符设备
	rtc_sysfs_init(rtc_class);//创建sysfs相关的文件
	return 0;
}

/* 平台设备驱动的初始化*/
Rtc-omap.c (drivers\rtc):module_init(rtc_init);

static int __init rtc_init(void)
{
	return platform_driver_probe(&omap_rtc_driver, omap_rtc_probe);
}

platform_driver_register,向platform这个虚拟总线上注册omap-rtc驱动，在setup_arch这个函数里面会调用platform_add_device,所以在总线上有omap-rtc设备，它们之间在"bus,device,device_driver"这个框架的设计下相遇，然后进行probe,分配相应的数据结构(struct rtc_device),向内核注册此数据结构。

 * platform_driver_probe - register driver for non-hotpluggable device
 * @drv: platform driver structure
 * @probe: the driver probe routine, probably from an __init section
 *
 * Use this instead of platform_driver_register() when you know the device
 * is not hotpluggable and has already been registered, and you want to
 * remove its run-once probe() infrastructure from memory after the driver
 * has bound to the device.
 *
 * One typical use for this would be with drivers for controllers integrated
 * into system-on-chip processors, where the controller devices have been
 * configured as part of board setup.
 *
 * Returns zero if the driver registered and bound to a device, else returns
 * a negative error code and with the driver not registered.
 */
int __init_or_module platform_driver_probe(struct platform_driver *drv,
		int (*probe)(struct platform_device *))
{
	int retval, code;

	/* make sure driver won't have bind/unbind attributes */
	drv->driver.suppress_bind_attrs = true;

	/* temporary section violation during probe() */
	drv->probe = probe;
	retval = code = platform_driver_register(drv);

	/*
	 * Fixup that section violation, being paranoid about code scanning
	 * the list of drivers in order to probe new devices.  Check to see
	 * if the probe was successful, and make sure any forced probes of
	 * new devices fail.
	 */
	spin_lock(&drv->driver.bus->p->klist_drivers.k_lock);
	drv->probe = NULL;
	if (code == 0 && list_empty(&drv->driver.p->klist_devices.k_list))
		retval = -ENODEV;
	drv->driver.probe = platform_drv_probe_fail;
	spin_unlock(&drv->driver.bus->p->klist_drivers.k_lock);

	if (code != retval)
		platform_driver_unregister(drv);
	return retval;
}

static int __init omap_rtc_probe(struct platform_device *pdev)
{
	struct resource		*res, *mem;
	struct rtc_device	*rtc;
	u8			reg, new_ctrl;

	omap_rtc_timer = platform_get_irq(pdev, 0);//获取滴答中断号
	if (omap_rtc_timer <= 0) {
		pr_debug("%s: no update irq?\n", pdev->name);
		return -ENOENT;
	}

	omap_rtc_alarm = platform_get_irq(pdev, 1);//获取报警中断号
	if (omap_rtc_alarm <= 0) {
		pr_debug("%s: no alarm irq?\n", pdev->name);
		return -ENOENT;
	}

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);//得到IO内存资源信息
	if (!res) {
		pr_debug("%s: RTC resource data missing\n", pdev->name);
		return -ENOENT;
	}

	mem = request_mem_region(res->start, resource_size(res), pdev->name);//申请IO内存资源
	if (!mem) {
		pr_debug("%s: RTC registers at %08x are not free\n",
			pdev->name, res->start);
		return -EBUSY;
	}

	rtc_base = ioremap(res->start, resource_size(res));//完成IO内存资源的映射
	if (!rtc_base) {
		pr_debug("%s: RTC registers can't be mapped\n", pdev->name);
		goto fail;
	}

	rtc = rtc_device_register(pdev->name, &pdev->dev,
			&omap_rtc_ops, THIS_MODULE);//分配struct rtc_device结构
	if (IS_ERR(rtc)) {
		pr_debug("%s: can't register RTC device, err %ld\n",
			pdev->name, PTR_ERR(rtc));
		goto fail0;
	}
	platform_set_drvdata(pdev, rtc);//设置平台设备驱动数据是struct rtc_device的指针
	dev_set_drvdata(&rtc->dev, mem);

	/* clear pending irqs, and set 1/second periodic,
	 * which we'll use instead of update irqs
	 */
	rtc_write(0, OMAP_RTC_INTERRUPTS_REG);

	/* clear old status */
	reg = rtc_read(OMAP_RTC_STATUS_REG);
	if (reg & (u8) OMAP_RTC_STATUS_POWER_UP) {
		pr_info("%s: RTC power up reset detected\n",
			pdev->name);
		rtc_write(OMAP_RTC_STATUS_POWER_UP, OMAP_RTC_STATUS_REG);
	}
	if (reg & (u8) OMAP_RTC_STATUS_ALARM)
		rtc_write(OMAP_RTC_STATUS_ALARM, OMAP_RTC_STATUS_REG);

	/* handle periodic and alarm irqs */
	if (request_irq(omap_rtc_timer, rtc_irq, IRQF_DISABLED,
			dev_name(&rtc->dev), rtc)) {
		pr_debug("%s: RTC timer interrupt IRQ%d already claimed\n",
			pdev->name, omap_rtc_timer);
		goto fail1;
	}
	if ((omap_rtc_timer != omap_rtc_alarm) &&
		(request_irq(omap_rtc_alarm, rtc_irq, IRQF_DISABLED,
			dev_name(&rtc->dev), rtc))) {
		pr_debug("%s: RTC alarm interrupt IRQ%d already claimed\n",
			pdev->name, omap_rtc_alarm);
		goto fail2;
	}

	/* On boards with split power, RTC_ON_NOFF won't reset the RTC */
	reg = rtc_read(OMAP_RTC_CTRL_REG);
	if (reg & (u8) OMAP_RTC_CTRL_STOP)
		pr_info("%s: already running\n", pdev->name);

	/* force to 24 hour mode */
	new_ctrl = reg & (OMAP_RTC_CTRL_SPLIT|OMAP_RTC_CTRL_AUTO_COMP);
	new_ctrl |= OMAP_RTC_CTRL_STOP;

	/* BOARD-SPECIFIC CUSTOMIZATION CAN GO HERE:
	 *
	 *  - Device wake-up capability setting should come through chip
	 *    init logic. OMAP1 boards should initialize the "wakeup capable"
	 *    flag in the platform device if the board is wired right for
	 *    being woken up by RTC alarm. For OMAP-L138, this capability
	 *    is built into the SoC by the "Deep Sleep" capability.
	 *
	 *  - Boards wired so RTC_ON_nOFF is used as the reset signal,
	 *    rather than nPWRON_RESET, should forcibly enable split
	 *    power mode.  (Some chip errata report that RTC_CTRL_SPLIT
	 *    is write-only, and always reads as zero...)
	 */

	if (new_ctrl & (u8) OMAP_RTC_CTRL_SPLIT)
		pr_info("%s: split power mode\n", pdev->name);

	if (reg != new_ctrl)
		rtc_write(new_ctrl, OMAP_RTC_CTRL_REG);

	if ((unsigned int)pdev->dev.platform_data == true)
		device_init_wakeup(&pdev->dev, 1);

	return 0;

fail2:
	free_irq(omap_rtc_timer, rtc);
fail1:
	rtc_device_unregister(rtc);
fail0:
	iounmap(rtc_base);
fail:
	release_mem_region(mem->start, resource_size(mem));
	return -EIO;
}

/* 在启动阶段初始化系统时钟*/
Hctosys.c (drivers\rtc):late_initcall(rtc_hctosys)

static int __init rtc_hctosys(void)
{
	int err = -ENODEV;
	struct rtc_time tm;
	struct timespec tv = {
		.tv_nsec = NSEC_PER_SEC >> 1,
	};
	struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);

	if (rtc == NULL) {
		pr_err("%s: unable to open rtc device (%s)\n",
			__FILE__, CONFIG_RTC_HCTOSYS_DEVICE);
		goto err_open;
	}

	err = rtc_read_time(rtc, &tm);
	if (err) {
		dev_err(rtc->dev.parent,
			"hctosys: unable to read the hardware clock\n");
		goto err_read;

	}

	err = rtc_valid_tm(&tm);
	if (err) {
		dev_err(rtc->dev.parent,
			"hctosys: invalid date/time\n");
		goto err_invalid;
	}

	rtc_tm_to_time(&tm, &tv.tv_sec);

	do_settimeofday(&tv);

	dev_info(rtc->dev.parent,
		"setting system clock to "
		"%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
		tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
		tm.tm_hour, tm.tm_min, tm.tm_sec,
		(unsigned int) tv.tv_sec);

err_invalid:
err_read:
	rtc_class_close(rtc);

err_open:
	rtc_hctosys_ret = err;

	return err;
}