remarkable-linux/drivers/clocksource/tcb_clksrc.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/irq.h>

#include <linux/clk.h>
#include <linux/err.h>
#include <linux/ioport.h>
#include <linux/io.h>
#include <linux/platform_device.h>
#include <linux/syscore_ops.h>
#include <linux/atmel_tc.h>


/*
 * We're configured to use a specific TC block, one that's not hooked
 * up to external hardware, to provide a time solution:
 *
 *   - Two channels combine to create a free-running 32 bit counter
 *     with a base rate of 5+ MHz, packaged as a clocksource (with
 *     resolution better than 200 nsec).
 *   - Some chips support 32 bit counter. A single channel is used for
 *     this 32 bit free-running counter. the second channel is not used.
 *
 *   - The third channel may be used to provide a 16-bit clockevent
 *     source, used in either periodic or oneshot mode.  This runs
 *     at 32 KiHZ, and can handle delays of up to two seconds.
 *
 * A boot clocksource and clockevent source are also currently needed,
 * unless the relevant platforms (ARM/AT91, AVR32/AT32) are changed so
 * this code can be used when init_timers() is called, well before most
 * devices are set up.  (Some low end AT91 parts, which can run uClinux,
 * have only the timers in one TC block... they currently don't support
 * the tclib code, because of that initialization issue.)
 *
 * REVISIT behavior during system suspend states... we should disable
 * all clocks and save the power.  Easily done for clockevent devices,
 * but clocksources won't necessarily get the needed notifications.
 * For deeper system sleep states, this will be mandatory...
 */

static void __iomem *tcaddr;
static struct
{
	u32 cmr;
	u32 imr;
	u32 rc;
	bool clken;
} tcb_cache[3];
static u32 bmr_cache;

static u64 tc_get_cycles(struct clocksource *cs)
{
	unsigned long	flags;
	u32		lower, upper;

	raw_local_irq_save(flags);
	do {
		upper = readl_relaxed(tcaddr + ATMEL_TC_REG(1, CV));
		lower = readl_relaxed(tcaddr + ATMEL_TC_REG(0, CV));
	} while (upper != readl_relaxed(tcaddr + ATMEL_TC_REG(1, CV)));

	raw_local_irq_restore(flags);
	return (upper << 16) | lower;
}

static u64 tc_get_cycles32(struct clocksource *cs)
{
	return readl_relaxed(tcaddr + ATMEL_TC_REG(0, CV));
}

void tc_clksrc_suspend(struct clocksource *cs)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(tcb_cache); i++) {
		tcb_cache[i].cmr = readl(tcaddr + ATMEL_TC_REG(i, CMR));
		tcb_cache[i].imr = readl(tcaddr + ATMEL_TC_REG(i, IMR));
		tcb_cache[i].rc = readl(tcaddr + ATMEL_TC_REG(i, RC));
		tcb_cache[i].clken = !!(readl(tcaddr + ATMEL_TC_REG(i, SR)) &
					ATMEL_TC_CLKSTA);
	}

	bmr_cache = readl(tcaddr + ATMEL_TC_BMR);
}

void tc_clksrc_resume(struct clocksource *cs)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(tcb_cache); i++) {
		/* Restore registers for the channel, RA and RB are not used  */
		writel(tcb_cache[i].cmr, tcaddr + ATMEL_TC_REG(i, CMR));
		writel(tcb_cache[i].rc, tcaddr + ATMEL_TC_REG(i, RC));
		writel(0, tcaddr + ATMEL_TC_REG(i, RA));
		writel(0, tcaddr + ATMEL_TC_REG(i, RB));
		/* Disable all the interrupts */
		writel(0xff, tcaddr + ATMEL_TC_REG(i, IDR));
		/* Reenable interrupts that were enabled before suspending */
		writel(tcb_cache[i].imr, tcaddr + ATMEL_TC_REG(i, IER));
		/* Start the clock if it was used */
		if (tcb_cache[i].clken)
			writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(i, CCR));
	}

	/* Dual channel, chain channels */
	writel(bmr_cache, tcaddr + ATMEL_TC_BMR);
	/* Finally, trigger all the channels*/
	writel(ATMEL_TC_SYNC, tcaddr + ATMEL_TC_BCR);
}

static struct clocksource clksrc = {
	.name           = "tcb_clksrc",
	.rating         = 200,
	.read           = tc_get_cycles,
	.mask           = CLOCKSOURCE_MASK(32),
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
	.suspend	= tc_clksrc_suspend,
	.resume		= tc_clksrc_resume,
};

#ifdef CONFIG_GENERIC_CLOCKEVENTS

struct tc_clkevt_device {
	struct clock_event_device	clkevt;
	struct clk			*clk;
	void __iomem			*regs;
};

static struct tc_clkevt_device *to_tc_clkevt(struct clock_event_device *clkevt)
{
	return container_of(clkevt, struct tc_clkevt_device, clkevt);
}

/* For now, we always use the 32K clock ... this optimizes for NO_HZ,
 * because using one of the divided clocks would usually mean the
 * tick rate can never be less than several dozen Hz (vs 0.5 Hz).
 *
 * A divided clock could be good for high resolution timers, since
 * 30.5 usec resolution can seem "low".
 */
static u32 timer_clock;

static int tc_shutdown(struct clock_event_device *d)
{
	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
	void __iomem		*regs = tcd->regs;

	writel(0xff, regs + ATMEL_TC_REG(2, IDR));
	writel(ATMEL_TC_CLKDIS, regs + ATMEL_TC_REG(2, CCR));
	if (!clockevent_state_detached(d))
		clk_disable(tcd->clk);

	return 0;
}

static int tc_set_oneshot(struct clock_event_device *d)
{
	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
	void __iomem		*regs = tcd->regs;

	if (clockevent_state_oneshot(d) || clockevent_state_periodic(d))
		tc_shutdown(d);

	clk_enable(tcd->clk);

	/* slow clock, count up to RC, then irq and stop */
	writel(timer_clock | ATMEL_TC_CPCSTOP | ATMEL_TC_WAVE |
		     ATMEL_TC_WAVESEL_UP_AUTO, regs + ATMEL_TC_REG(2, CMR));
	writel(ATMEL_TC_CPCS, regs + ATMEL_TC_REG(2, IER));

	/* set_next_event() configures and starts the timer */
	return 0;
}

static int tc_set_periodic(struct clock_event_device *d)
{
	struct tc_clkevt_device *tcd = to_tc_clkevt(d);
	void __iomem		*regs = tcd->regs;

	if (clockevent_state_oneshot(d) || clockevent_state_periodic(d))
		tc_shutdown(d);

	/* By not making the gentime core emulate periodic mode on top
	 * of oneshot, we get lower overhead and improved accuracy.
	 */
	clk_enable(tcd->clk);

	/* slow clock, count up to RC, then irq and restart */
	writel(timer_clock | ATMEL_TC_WAVE | ATMEL_TC_WAVESEL_UP_AUTO,
		     regs + ATMEL_TC_REG(2, CMR));
	writel((32768 + HZ / 2) / HZ, tcaddr + ATMEL_TC_REG(2, RC));

	/* Enable clock and interrupts on RC compare */
	writel(ATMEL_TC_CPCS, regs + ATMEL_TC_REG(2, IER));

	/* go go gadget! */
	writel(ATMEL_TC_CLKEN | ATMEL_TC_SWTRG, regs +
		     ATMEL_TC_REG(2, CCR));
	return 0;
}

static int tc_next_event(unsigned long delta, struct clock_event_device *d)
{
	writel_relaxed(delta, tcaddr + ATMEL_TC_REG(2, RC));

	/* go go gadget! */
	writel_relaxed(ATMEL_TC_CLKEN | ATMEL_TC_SWTRG,
			tcaddr + ATMEL_TC_REG(2, CCR));
	return 0;
}

static struct tc_clkevt_device clkevt = {
	.clkevt	= {
		.name			= "tc_clkevt",
		.features		= CLOCK_EVT_FEAT_PERIODIC |
					  CLOCK_EVT_FEAT_ONESHOT,
		/* Should be lower than at91rm9200's system timer */
		.rating			= 125,
		.set_next_event		= tc_next_event,
		.set_state_shutdown	= tc_shutdown,
		.set_state_periodic	= tc_set_periodic,
		.set_state_oneshot	= tc_set_oneshot,
	},
};

static irqreturn_t ch2_irq(int irq, void *handle)
{
	struct tc_clkevt_device	*dev = handle;
	unsigned int		sr;

	sr = readl_relaxed(dev->regs + ATMEL_TC_REG(2, SR));
	if (sr & ATMEL_TC_CPCS) {
		dev->clkevt.event_handler(&dev->clkevt);
		return IRQ_HANDLED;
	}

	return IRQ_NONE;
}

static int __init setup_clkevents(struct atmel_tc *tc, int clk32k_divisor_idx)
{
	int ret;
	struct clk *t2_clk = tc->clk[2];
	int irq = tc->irq[2];

	ret = clk_prepare_enable(tc->slow_clk);
	if (ret)
		return ret;

	/* try to enable t2 clk to avoid future errors in mode change */
	ret = clk_prepare_enable(t2_clk);
	if (ret) {
		clk_disable_unprepare(tc->slow_clk);
		return ret;
	}

	clk_disable(t2_clk);

	clkevt.regs = tc->regs;
	clkevt.clk = t2_clk;

	timer_clock = clk32k_divisor_idx;

	clkevt.clkevt.cpumask = cpumask_of(0);

	ret = request_irq(irq, ch2_irq, IRQF_TIMER, "tc_clkevt", &clkevt);
	if (ret) {
		clk_unprepare(t2_clk);
		clk_disable_unprepare(tc->slow_clk);
		return ret;
	}

	clockevents_config_and_register(&clkevt.clkevt, 32768, 1, 0xffff);

	return ret;
}

#else /* !CONFIG_GENERIC_CLOCKEVENTS */

static int __init setup_clkevents(struct atmel_tc *tc, int clk32k_divisor_idx)
{
	/* NOTHING */
	return 0;
}

#endif

static void __init tcb_setup_dual_chan(struct atmel_tc *tc, int mck_divisor_idx)
{
	/* channel 0:  waveform mode, input mclk/8, clock TIOA0 on overflow */
	writel(mck_divisor_idx			/* likely divide-by-8 */
			| ATMEL_TC_WAVE
			| ATMEL_TC_WAVESEL_UP		/* free-run */
			| ATMEL_TC_ACPA_SET		/* TIOA0 rises at 0 */
			| ATMEL_TC_ACPC_CLEAR,		/* (duty cycle 50%) */
			tcaddr + ATMEL_TC_REG(0, CMR));
	writel(0x0000, tcaddr + ATMEL_TC_REG(0, RA));
	writel(0x8000, tcaddr + ATMEL_TC_REG(0, RC));
	writel(0xff, tcaddr + ATMEL_TC_REG(0, IDR));	/* no irqs */
	writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(0, CCR));

	/* channel 1:  waveform mode, input TIOA0 */
	writel(ATMEL_TC_XC1			/* input: TIOA0 */
			| ATMEL_TC_WAVE
			| ATMEL_TC_WAVESEL_UP,		/* free-run */
			tcaddr + ATMEL_TC_REG(1, CMR));
	writel(0xff, tcaddr + ATMEL_TC_REG(1, IDR));	/* no irqs */
	writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(1, CCR));

	/* chain channel 0 to channel 1*/
	writel(ATMEL_TC_TC1XC1S_TIOA0, tcaddr + ATMEL_TC_BMR);
	/* then reset all the timers */
	writel(ATMEL_TC_SYNC, tcaddr + ATMEL_TC_BCR);
}

static void __init tcb_setup_single_chan(struct atmel_tc *tc, int mck_divisor_idx)
{
	/* channel 0:  waveform mode, input mclk/8 */
	writel(mck_divisor_idx			/* likely divide-by-8 */
			| ATMEL_TC_WAVE
			| ATMEL_TC_WAVESEL_UP,		/* free-run */
			tcaddr + ATMEL_TC_REG(0, CMR));
	writel(0xff, tcaddr + ATMEL_TC_REG(0, IDR));	/* no irqs */
	writel(ATMEL_TC_CLKEN, tcaddr + ATMEL_TC_REG(0, CCR));

	/* then reset all the timers */
	writel(ATMEL_TC_SYNC, tcaddr + ATMEL_TC_BCR);
}

static int __init tcb_clksrc_init(void)
{
	static char bootinfo[] __initdata
		= KERN_DEBUG "%s: tc%d at %d.%03d MHz\n";

	struct platform_device *pdev;
	struct atmel_tc *tc;
	struct clk *t0_clk;
	u32 rate, divided_rate = 0;
	int best_divisor_idx = -1;
	int clk32k_divisor_idx = -1;
	int i;
	int ret;

	tc = atmel_tc_alloc(CONFIG_ATMEL_TCB_CLKSRC_BLOCK);
	if (!tc) {
		pr_debug("can't alloc TC for clocksource\n");
		return -ENODEV;
	}
	tcaddr = tc->regs;
	pdev = tc->pdev;

	t0_clk = tc->clk[0];
	ret = clk_prepare_enable(t0_clk);
	if (ret) {
		pr_debug("can't enable T0 clk\n");
		goto err_free_tc;
	}

	/* How fast will we be counting?  Pick something over 5 MHz.  */
	rate = (u32) clk_get_rate(t0_clk);
	for (i = 0; i < 5; i++) {
		unsigned divisor = atmel_tc_divisors[i];
		unsigned tmp;

		/* remember 32 KiHz clock for later */
		if (!divisor) {
			clk32k_divisor_idx = i;
			continue;
		}

		tmp = rate / divisor;
		pr_debug("TC: %u / %-3u [%d] --> %u\n", rate, divisor, i, tmp);
		if (best_divisor_idx > 0) {
			if (tmp < 5 * 1000 * 1000)
				continue;
		}
		divided_rate = tmp;
		best_divisor_idx = i;
	}


	printk(bootinfo, clksrc.name, CONFIG_ATMEL_TCB_CLKSRC_BLOCK,
			divided_rate / 1000000,
			((divided_rate + 500000) % 1000000) / 1000);

	if (tc->tcb_config && tc->tcb_config->counter_width == 32) {
		/* use apropriate function to read 32 bit counter */
		clksrc.read = tc_get_cycles32;
		/* setup ony channel 0 */
		tcb_setup_single_chan(tc, best_divisor_idx);
	} else {
		/* tclib will give us three clocks no matter what the
		 * underlying platform supports.
		 */
		ret = clk_prepare_enable(tc->clk[1]);
		if (ret) {
			pr_debug("can't enable T1 clk\n");
			goto err_disable_t0;
		}
		/* setup both channel 0 & 1 */
		tcb_setup_dual_chan(tc, best_divisor_idx);
	}

	/* and away we go! */
	ret = clocksource_register_hz(&clksrc, divided_rate);
	if (ret)
		goto err_disable_t1;

	/* channel 2:  periodic and oneshot timer support */
	ret = setup_clkevents(tc, clk32k_divisor_idx);
	if (ret)
		goto err_unregister_clksrc;

	return 0;

err_unregister_clksrc:
	clocksource_unregister(&clksrc);

err_disable_t1:
	if (!tc->tcb_config || tc->tcb_config->counter_width != 32)
		clk_disable_unprepare(tc->clk[1]);

err_disable_t0:
	clk_disable_unprepare(t0_clk);

err_free_tc:
	atmel_tc_free(tc);
	return ret;
}
arch_initcall(tcb_clksrc_init);