Simplified MC146818 RTC Linux driver

rtc.c

/*
 * RTC class driver for "CMOS RTC":  PCs, ACPI, etc
 *
 * Copyright (C) 1996 Paul Gortmaker (drivers/char/rtc.c)
 * Copyright (C) 2006 David Brownell (convert to new framework)
 *
 * 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.
 */

/*
 * The original "cmos clock" chip was an MC146818 chip, now obsolete.
 * That defined the register interface now provided by all PCs, some
 * non-PC systems, and incorporated into ACPI.  Modern PC chipsets
 * integrate an MC146818 clone in their southbridge, and boards use
 * that instead of discrete clones like the DS12887 or M48T86.  There
 * are also clones that connect using the LPC bus.
 *
 * That register API is also used directly by various other drivers
 * (notably for integrated NVRAM), infrastructure (x86 has code to
 * bypass the RTC framework, directly reading the RTC during boot
 * and updating minutes/seconds for systems using NTP synch) and
 * utilities (like userspace 'hwclock', if no /dev node exists).
 *
 * So **ALL** calls to CMOS_READ and CMOS_WRITE must be done with
 * interrupts disabled, holding the global rtc_lock, to exclude those
 * other drivers and utilities on correctly configured systems.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/log2.h>

/* this is for "generic access to PC-style RTC" using CMOS_READ/CMOS_WRITE */
#include <linux/mc146818rtc.h>

struct cmos_rtc {
	struct rtc_device	*rtc;
	struct device		*dev;
	int			irq;
	struct resource		*iomem;
	time64_t		alarm_expires;

	void			(*wake_on)(struct device *);
	void			(*wake_off)(struct device *);

	u8			enabled_wake;
	u8			suspend_ctrl;

	/* newer hardware extends the original register set */
	u8			day_alrm;
	u8			mon_alrm;
	u8			century;
};

/* both platform and pnp busses use negative numbers for invalid irqs */
#define is_valid_irq(n)		((n) > 0)

static const char driver_name[] = "rtc_thho_show_in_dmesg";

/* The RTC_INTR register may have e.g. RTC_PF set even if RTC_PIE is clear;
 * always mask it against the irq enable bits in RTC_CONTROL.  Bit values
 * are the same: PF==PIE, AF=AIE, UF=UIE; so RTC_IRQMASK works with both.
 */
#define	RTC_IRQMASK	(RTC_PF | RTC_AF | RTC_UF)

static inline int is_intr(u8 rtc_intr)
{
	if (!(rtc_intr & RTC_IRQF))
		return 0;
	return rtc_intr & RTC_IRQMASK;
}

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

/* Much modern x86 hardware has HPETs (10+ MHz timers) which, because
 * many BIOS programmers don't set up "sane mode" IRQ routing, are mostly
 * used in a broken "legacy replacement" mode.  The breakage includes
 * HPET #1 hijacking the IRQ for this RTC, and being unavailable for
 * other (better) use.
 *
 * When that broken mode is in use, platform glue provides a partial
 * emulation of hardware RTC IRQ facilities using HPET #1.  We don't
 * want to use HPET for anything except those IRQs though...
 */
#include <asm/hpet.h>

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

static int cmos_read_time(struct device *dev, struct rtc_time *t)
{
	/* REVISIT:  if the clock has a "century" register, use
	 * that instead of the heuristic in mc146818_get_time().
	 * That'll make Y3K compatility (year > 2070) easy!
	 */
	printk("My Debugger: cmos_read_time is called.\n");
	mc146818_get_time(t);
	return 0;
}

static void cmos_checkintr(struct cmos_rtc *cmos, unsigned char rtc_control)
{
	unsigned char	rtc_intr;
	printk("My Debugger: cmos_checkintr is called.\n");

	/* NOTE after changing RTC_xIE bits we always read INTR_FLAGS;
	 * allegedly some older rtcs need that to handle irqs properly
	 */
	rtc_intr = CMOS_READ(RTC_INTR_FLAGS);

	if (is_hpet_enabled())
		return;

	rtc_intr &= (rtc_control & RTC_IRQMASK) | RTC_IRQF;
	if (is_intr(rtc_intr))
		rtc_update_irq(cmos->rtc, 1, rtc_intr);
}

static void cmos_irq_enable(struct cmos_rtc *cmos, unsigned char mask)
{
	unsigned char	rtc_control;

	/* flush any pending IRQ status, notably for update irqs,
	 * before we enable new IRQs
	 */
	printk("My Debugger: cmos_irq_enable is called.\n");
	rtc_control = CMOS_READ(RTC_CONTROL);
	cmos_checkintr(cmos, rtc_control);

	rtc_control |= mask;
	CMOS_WRITE(rtc_control, RTC_CONTROL);
	hpet_set_rtc_irq_bit(mask);

	cmos_checkintr(cmos, rtc_control);
}

static void cmos_irq_disable(struct cmos_rtc *cmos, unsigned char mask)
{
	unsigned char	rtc_control;
	printk("My Debugger: cmos_irq_disable is called.\n");

	rtc_control = CMOS_READ(RTC_CONTROL);
	rtc_control &= ~mask;
	CMOS_WRITE(rtc_control, RTC_CONTROL);
	hpet_mask_rtc_irq_bit(mask);

	cmos_checkintr(cmos, rtc_control);
}

static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
{
	struct cmos_rtc	*cmos = dev_get_drvdata(dev);
	unsigned char mon, mday, hrs, min, sec, rtc_control;
	printk("My Debugger: cmos_set_alarm is called.\n");

	if (!is_valid_irq(cmos->irq))
		return -EIO;

	mon = t->time.tm_mon + 1;
	mday = t->time.tm_mday;
	hrs = t->time.tm_hour;
	min = t->time.tm_min;
	sec = t->time.tm_sec;

	rtc_control = CMOS_READ(RTC_CONTROL);
	if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
		/* Writing 0xff means "don't care" or "match all".  */
		mon = (mon <= 12) ? bin2bcd(mon) : 0xff;
		mday = (mday >= 1 && mday <= 31) ? bin2bcd(mday) : 0xff;
		hrs = (hrs < 24) ? bin2bcd(hrs) : 0xff;
		min = (min < 60) ? bin2bcd(min) : 0xff;
		sec = (sec < 60) ? bin2bcd(sec) : 0xff;
	}

	spin_lock_irq(&rtc_lock);

	/* next rtc irq must not be from previous alarm setting */
	cmos_irq_disable(cmos, RTC_AIE);

	/* update alarm */
	CMOS_WRITE(hrs, RTC_HOURS_ALARM);
	CMOS_WRITE(min, RTC_MINUTES_ALARM);
	CMOS_WRITE(sec, RTC_SECONDS_ALARM);

	/* the system may support an "enhanced" alarm */
	if (cmos->day_alrm) {
		CMOS_WRITE(mday, cmos->day_alrm);
		if (cmos->mon_alrm)
			CMOS_WRITE(mon, cmos->mon_alrm);
	}

	/* FIXME the HPET alarm glue currently ignores day_alrm
	 * and mon_alrm ...
	 */
	hpet_set_alarm_time(t->time.tm_hour, t->time.tm_min, t->time.tm_sec);

	if (t->enabled)
		cmos_irq_enable(cmos, RTC_AIE);

	spin_unlock_irq(&rtc_lock);

	cmos->alarm_expires = rtc_tm_to_time64(&t->time);

	printk("My Debugger: cmos_set_alarm is called. done.\n");
	return 0;
}

static const struct rtc_class_ops cmos_rtc_ops = {
	.read_time		= cmos_read_time,
	.set_alarm		= cmos_set_alarm,
};

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

static struct cmos_rtc	cmos_rtc;

static irqreturn_t cmos_interrupt(int irq, void *p)
{
	u8		irqstat;
	u8		rtc_control;
	printk("My Debugger: cmos_interrupt is called.\n");

	spin_lock(&rtc_lock);

	/* When the HPET interrupt handler calls us, the interrupt
	 * status is passed as arg1 instead of the irq number.  But
	 * always clear irq status, even when HPET is in the way.
	 *
	 * Note that HPET and RTC are almost certainly out of phase,
	 * giving different IRQ status ...
	 */
	irqstat = CMOS_READ(RTC_INTR_FLAGS);
	rtc_control = CMOS_READ(RTC_CONTROL);
	if (is_hpet_enabled())
		irqstat = (unsigned long)irq & 0xF0;

	/* If we were suspended, RTC_CONTROL may not be accurate since the
	 * bios may have cleared it.
	 */
	if (!cmos_rtc.suspend_ctrl)
		irqstat &= (rtc_control & RTC_IRQMASK) | RTC_IRQF;
	else
		irqstat &= (cmos_rtc.suspend_ctrl & RTC_IRQMASK) | RTC_IRQF;

	/* All Linux RTC alarms should be treated as if they were oneshot.
	 * Similar code may be needed in system wakeup paths, in case the
	 * alarm woke the system.
	 */
	if (irqstat & RTC_AIE) {
		cmos_rtc.suspend_ctrl &= ~RTC_AIE;
		rtc_control &= ~RTC_AIE;
		CMOS_WRITE(rtc_control, RTC_CONTROL);
		hpet_mask_rtc_irq_bit(RTC_AIE);
		CMOS_READ(RTC_INTR_FLAGS);
	}
	spin_unlock(&rtc_lock);

	if (is_intr(irqstat)) {
		rtc_update_irq(p, 1, irqstat);
		return IRQ_HANDLED;
	} else
		return IRQ_NONE;
}

#ifdef	CONFIG_PNP
#define	INITSECTION

#else
#define	INITSECTION	__init
#endif

static int INITSECTION
cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
{
	struct cmos_rtc_board_info	*info = dev_get_platdata(dev);
	int				retval = 0;
	unsigned char			rtc_control;
	unsigned			address_space;
	u32				flags = 0;

	printk("My Debugger: cmos_do_probe\n");
	/* there can be only one ... */
	if (cmos_rtc.dev)
		return -EBUSY;

	if (!ports)
		return -ENODEV;

	/* Claim I/O ports ASAP, minimizing conflict with legacy driver.
	 *
	 * REVISIT non-x86 systems may instead use memory space resources
	 * (needing ioremap etc), not i/o space resources like this ...
	 */
	if (RTC_IOMAPPED)
		ports = request_region(ports->start, resource_size(ports),
				       driver_name);
	else
		ports = request_mem_region(ports->start, resource_size(ports),
					   driver_name);
	if (!ports) {
		dev_dbg(dev, "i/o registers already in use\n");
		return -EBUSY;
	}

	cmos_rtc.irq = rtc_irq;
	cmos_rtc.iomem = ports;

	/* Heuristic to deduce NVRAM size ... do what the legacy NVRAM
	 * driver did, but don't reject unknown configs.   Old hardware
	 * won't address 128 bytes.  Newer chips have multiple banks,
	 * though they may not be listed in one I/O resource.
	 */
	address_space = 128;

	/* For ACPI systems extension info comes from the FADT.  On others,
	 * board specific setup provides it as appropriate.  Systems where
	 * the alarm IRQ isn't automatically a wakeup IRQ (like ACPI, and
	 * some almost-clones) can provide hooks to make that behave.
	 *
	 * Note that ACPI doesn't preclude putting these registers into
	 * "extended" areas of the chip, including some that we won't yet
	 * expect CMOS_READ and friends to handle.
	 */
	if (info) {
		if (info->flags)
			flags = info->flags;
		if (info->address_space)
			address_space = info->address_space;

		if (info->rtc_day_alarm && info->rtc_day_alarm < 128)
			cmos_rtc.day_alrm = info->rtc_day_alarm;
		if (info->rtc_mon_alarm && info->rtc_mon_alarm < 128)
			cmos_rtc.mon_alrm = info->rtc_mon_alarm;
		if (info->rtc_century && info->rtc_century < 128)
			cmos_rtc.century = info->rtc_century;

		if (info->wake_on && info->wake_off) {
			cmos_rtc.wake_on = info->wake_on;
			cmos_rtc.wake_off = info->wake_off;
		}
	}

	cmos_rtc.dev = dev;
	dev_set_drvdata(dev, &cmos_rtc);

	cmos_rtc.rtc = rtc_device_register(driver_name, dev,
				&cmos_rtc_ops, THIS_MODULE);
	if (IS_ERR(cmos_rtc.rtc)) {
		retval = PTR_ERR(cmos_rtc.rtc);
		goto cleanup0;
	}

	rename_region(ports, dev_name(&cmos_rtc.rtc->dev));

	spin_lock_irq(&rtc_lock);

	if (!(flags & CMOS_RTC_FLAGS_NOFREQ)) {
		/* force periodic irq to CMOS reset default of 1024Hz;
		 *
		 * REVISIT it's been reported that at least one x86_64 ALI
		 * mobo doesn't use 32KHz here ... for portability we might
		 * need to do something about other clock frequencies.
		 */
		cmos_rtc.rtc->irq_freq = 1024;
		hpet_set_periodic_freq(cmos_rtc.rtc->irq_freq);
		CMOS_WRITE(RTC_REF_CLCK_32KHZ | 0x06, RTC_FREQ_SELECT);
	}

	/* disable irqs */
	if (is_valid_irq(rtc_irq))
		cmos_irq_disable(&cmos_rtc, RTC_PIE | RTC_AIE | RTC_UIE);

	rtc_control = CMOS_READ(RTC_CONTROL);

	spin_unlock_irq(&rtc_lock);

	/* FIXME:
	 * <asm-generic/rtc.h> doesn't know 12-hour mode either.
	 */
	if (is_valid_irq(rtc_irq) && !(rtc_control & RTC_24H)) {
		dev_warn(dev, "only 24-hr supported\n");
		retval = -ENXIO;
		goto cleanup1;
	}

	if (is_valid_irq(rtc_irq)) {
		irq_handler_t rtc_int_handler;

		if (is_hpet_enabled()) {
			rtc_int_handler = hpet_rtc_interrupt;
			retval = hpet_register_irq_handler(cmos_interrupt);
			if (retval) {
				dev_warn(dev, "hpet_register_irq_handler "
						" failed in rtc_init().");
				goto cleanup1;
			}
		} else
			rtc_int_handler = cmos_interrupt;

		retval = request_irq(rtc_irq, rtc_int_handler,
				IRQF_SHARED, dev_name(&cmos_rtc.rtc->dev),
				cmos_rtc.rtc);
		if (retval < 0) {
			dev_dbg(dev, "IRQ %d is already in use\n", rtc_irq);
			goto cleanup1;
		}
	}
	hpet_rtc_timer_init();

	printk("My Debugger: cmos_do_probe done!\n");

	return 0;

cleanup1:
	cmos_rtc.dev = NULL;
	rtc_device_unregister(cmos_rtc.rtc);
cleanup0:
	if (RTC_IOMAPPED)
		release_region(ports->start, resource_size(ports));
	else
		release_mem_region(ports->start, resource_size(ports));
	return retval;
}

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

/* On non-x86 systems, a "CMOS" RTC lives most naturally on platform_bus.
 * ACPI systems always list these as PNPACPI devices, and pre-ACPI PCs
 * probably list them in similar PNPBIOS tables; so PNP is more common.
 *
 * We don't use legacy "poke at the hardware" probing.  Ancient PCs that
 * predate even PNPBIOS should set up platform_bus devices.
 */

#ifdef	CONFIG_PNP

#include <linux/pnp.h>

static int cmos_pnp_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
{
	// it seems there should be something as platform_data
	//(&pnp->dev)->platform_data = &acpi_rtc_info;
	(&pnp->dev)->platform_data = NULL;
	printk("My Debugger: cmos_pnp_probe\n");

	if (pnp_port_start(pnp, 0) == 0x70 && !pnp_irq_valid(pnp, 0))
		/* Some machines contain a PNP entry for the RTC, but
		 * don't define the IRQ. It should always be safe to
		 * hardcode it in these cases
		 */
		return cmos_do_probe(&pnp->dev,
				pnp_get_resource(pnp, IORESOURCE_IO, 0), 8);
	else
		return cmos_do_probe(&pnp->dev,
				pnp_get_resource(pnp, IORESOURCE_IO, 0),
				pnp_irq(pnp, 0));
	printk("My Debugger: cmos_pnp_probe. done!\n");
}

static void cmos_pnp_remove(struct pnp_dev *pnp)
{
	struct device *dev = &pnp->dev;
	struct cmos_rtc	*cmos = dev_get_drvdata(dev);
	struct resource *ports;

	cmos_do_shutdown(cmos->irq);

	if (is_valid_irq(cmos->irq)) {
		free_irq(cmos->irq, cmos->rtc);
		hpet_unregister_irq_handler(cmos_interrupt);
	}

	rtc_device_unregister(cmos->rtc);
	cmos->rtc = NULL;

	ports = cmos->iomem;
	if (RTC_IOMAPPED)
		release_region(ports->start, resource_size(ports));
	else
		release_mem_region(ports->start, resource_size(ports));
	cmos->iomem = NULL;

	cmos->dev = NULL;
}

static void cmos_pnp_shutdown(struct pnp_dev *pnp)
{
	struct device *dev = &pnp->dev;
	struct cmos_rtc	*cmos = dev_get_drvdata(dev);

	int rtc_irq = cmos->irq;
	spin_lock_irq(&rtc_lock);
	if (is_valid_irq(rtc_irq))
		cmos_irq_disable(&cmos_rtc, RTC_IRQMASK);
	spin_unlock_irq(&rtc_lock);
}

static const struct pnp_device_id rtc_ids[] = {
	{ .id = "PNP0b00", },
	{ .id = "PNP0b01", },
	{ .id = "PNP0b02", },
	{ },
};
MODULE_DEVICE_TABLE(pnp, rtc_ids);

static struct pnp_driver cmos_pnp_driver = {
	.name		= (char *) driver_name,
	.id_table	= rtc_ids,
	.probe		= cmos_pnp_probe,
	.remove		= cmos_pnp_remove,
	.shutdown	= cmos_pnp_shutdown,
};

#endif	/* CONFIG_PNP */

static bool pnp_driver_registered;

static int __init cmos_init(void)
{
	int retval = 0;

	printk("My Debugger: cmos_init.\n");
	printk("My Debugger: probe rtc...\n");
	printk("My Debugger: probe pnp rtc...\n");
	retval = pnp_register_driver(&cmos_pnp_driver);
	if (retval == 0)
		pnp_driver_registered = true;
	printk("My Debugger: probe pnp rtc ... retval %d\n", retval);

	if (retval == 0)
		return 0;

	if (pnp_driver_registered)
		pnp_unregister_driver(&cmos_pnp_driver);

	printk("My Debugger: cmos_init done.\n");
	return retval;
}
module_init(cmos_init);

static void __exit cmos_exit(void)
{
	printk("My Debugger: cmos_exit.\n");
	if (pnp_driver_registered)
		pnp_unregister_driver(&cmos_pnp_driver);
	printk("My Debugger: cmos_exit done.\n");
}
module_exit(cmos_exit);


MODULE_AUTHOR("David Brownell");
MODULE_DESCRIPTION("Driver for PC-style 'CMOS' RTCs");
MODULE_LICENSE("GPL");