WSL2-Linux-Kernel/drivers/clocksource/timer-ti-dm-systimer.c

// SPDX-License-Identifier: GPL-2.0+
#include <linux/clk.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/err.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/sched_clock.h>

#include <linux/clk/clk-conf.h>

#include <clocksource/timer-ti-dm.h>
#include <dt-bindings/bus/ti-sysc.h>

/* For type1, set SYSC_OMAP2_CLOCKACTIVITY for fck off on idle, l4 clock on */
#define DMTIMER_TYPE1_ENABLE	((1 << 9) | (SYSC_IDLE_SMART << 3) | \
				 SYSC_OMAP2_ENAWAKEUP | SYSC_OMAP2_AUTOIDLE)
#define DMTIMER_TYPE1_DISABLE	(SYSC_OMAP2_SOFTRESET | SYSC_OMAP2_AUTOIDLE)
#define DMTIMER_TYPE2_ENABLE	(SYSC_IDLE_SMART_WKUP << 2)
#define DMTIMER_RESET_WAIT	100000

#define DMTIMER_INST_DONT_CARE	~0U

static int counter_32k;
static u32 clocksource;
static u32 clockevent;

/*
 * Subset of the timer registers we use. Note that the register offsets
 * depend on the timer revision detected.
 */
struct dmtimer_systimer {
	void __iomem *base;
	u8 sysc;
	u8 irq_stat;
	u8 irq_ena;
	u8 pend;
	u8 load;
	u8 counter;
	u8 ctrl;
	u8 wakeup;
	u8 ifctrl;
	struct clk *fck;
	struct clk *ick;
	unsigned long rate;
};

struct dmtimer_clockevent {
	struct clock_event_device dev;
	struct dmtimer_systimer t;
	u32 period;
};

struct dmtimer_clocksource {
	struct clocksource dev;
	struct dmtimer_systimer t;
	unsigned int loadval;
};

/* Assumes v1 ip if bits [31:16] are zero */
static bool dmtimer_systimer_revision1(struct dmtimer_systimer *t)
{
	u32 tidr = readl_relaxed(t->base);

	return !(tidr >> 16);
}

static void dmtimer_systimer_enable(struct dmtimer_systimer *t)
{
	u32 val;

	if (dmtimer_systimer_revision1(t))
		val = DMTIMER_TYPE1_ENABLE;
	else
		val = DMTIMER_TYPE2_ENABLE;

	writel_relaxed(val, t->base + t->sysc);
}

static void dmtimer_systimer_disable(struct dmtimer_systimer *t)
{
	if (!dmtimer_systimer_revision1(t))
		return;

	writel_relaxed(DMTIMER_TYPE1_DISABLE, t->base + t->sysc);
}

static int __init dmtimer_systimer_type1_reset(struct dmtimer_systimer *t)
{
	void __iomem *syss = t->base + OMAP_TIMER_V1_SYS_STAT_OFFSET;
	int ret;
	u32 l;

	dmtimer_systimer_enable(t);
	writel_relaxed(BIT(1) | BIT(2), t->base + t->ifctrl);
	ret = readl_poll_timeout_atomic(syss, l, l & BIT(0), 100,
					DMTIMER_RESET_WAIT);

	return ret;
}

/* Note we must use io_base instead of func_base for type2 OCP regs */
static int __init dmtimer_systimer_type2_reset(struct dmtimer_systimer *t)
{
	void __iomem *sysc = t->base + t->sysc;
	u32 l;

	dmtimer_systimer_enable(t);
	l = readl_relaxed(sysc);
	l |= BIT(0);
	writel_relaxed(l, sysc);

	return readl_poll_timeout_atomic(sysc, l, !(l & BIT(0)), 100,
					 DMTIMER_RESET_WAIT);
}

static int __init dmtimer_systimer_reset(struct dmtimer_systimer *t)
{
	int ret;

	if (dmtimer_systimer_revision1(t))
		ret = dmtimer_systimer_type1_reset(t);
	else
		ret = dmtimer_systimer_type2_reset(t);
	if (ret < 0) {
		pr_err("%s failed with %i\n", __func__, ret);

		return ret;
	}

	return 0;
}

static const struct of_device_id counter_match_table[] = {
	{ .compatible = "ti,omap-counter32k" },
	{ /* Sentinel */ },
};

/*
 * Check if the SoC als has a usable working 32 KiHz counter. The 32 KiHz
 * counter is handled by timer-ti-32k, but we need to detect it as it
 * affects the preferred dmtimer system timer configuration. There is
 * typically no use for a dmtimer clocksource if the 32 KiHz counter is
 * present, except on am437x as described below.
 */
static void __init dmtimer_systimer_check_counter32k(void)
{
	struct device_node *np;

	if (counter_32k)
		return;

	np = of_find_matching_node(NULL, counter_match_table);
	if (!np) {
		counter_32k = -ENODEV;

		return;
	}

	if (of_device_is_available(np))
		counter_32k = 1;
	else
		counter_32k = -ENODEV;

	of_node_put(np);
}

static const struct of_device_id dmtimer_match_table[] = {
	{ .compatible = "ti,omap2420-timer", },
	{ .compatible = "ti,omap3430-timer", },
	{ .compatible = "ti,omap4430-timer", },
	{ .compatible = "ti,omap5430-timer", },
	{ .compatible = "ti,am335x-timer", },
	{ .compatible = "ti,am335x-timer-1ms", },
	{ .compatible = "ti,dm814-timer", },
	{ .compatible = "ti,dm816-timer", },
	{ /* Sentinel */ },
};

/*
 * Checks that system timers are configured to not reset and idle during
 * the generic timer-ti-dm device driver probe. And that the system timer
 * source clocks are properly configured. Also, let's not hog any DSP and
 * PWM capable timers unnecessarily as system timers.
 */
static bool __init dmtimer_is_preferred(struct device_node *np)
{
	if (!of_device_is_available(np))
		return false;

	if (!of_property_read_bool(np->parent,
				   "ti,no-reset-on-init"))
		return false;

	if (!of_property_read_bool(np->parent, "ti,no-idle"))
		return false;

	/* Secure gptimer12 is always clocked with a fixed source */
	if (!of_property_read_bool(np, "ti,timer-secure")) {
		if (!of_property_read_bool(np, "assigned-clocks"))
			return false;

		if (!of_property_read_bool(np, "assigned-clock-parents"))
			return false;
	}

	if (of_property_read_bool(np, "ti,timer-dsp"))
		return false;

	if (of_property_read_bool(np, "ti,timer-pwm"))
		return false;

	return true;
}

/*
 * Finds the first available usable always-on timer, and assigns it to either
 * clockevent or clocksource depending if the counter_32k is available on the
 * SoC or not.
 *
 * Some omap3 boards with unreliable oscillator must not use the counter_32k
 * or dmtimer1 with 32 KiHz source. Additionally, the boards with unreliable
 * oscillator should really set counter_32k as disabled, and delete dmtimer1
 * ti,always-on property, but let's not count on it. For these quirky cases,
 * we prefer using the always-on secure dmtimer12 with the internal 32 KiHz
 * clock as the clocksource, and any available dmtimer as clockevent.
 *
 * For am437x, we are using am335x style dmtimer clocksource. It is unclear
 * if this quirk handling is really needed, but let's change it separately
 * based on testing as it might cause side effects.
 */
static void __init dmtimer_systimer_assign_alwon(void)
{
	struct device_node *np;
	u32 pa = 0;
	bool quirk_unreliable_oscillator = false;

	/* Quirk unreliable 32 KiHz oscillator with incomplete dts */
	if (of_machine_is_compatible("ti,omap3-beagle") ||
	    of_machine_is_compatible("timll,omap3-devkit8000")) {
		quirk_unreliable_oscillator = true;
		counter_32k = -ENODEV;
	}

	/* Quirk am437x using am335x style dmtimer clocksource */
	if (of_machine_is_compatible("ti,am43"))
		counter_32k = -ENODEV;

	for_each_matching_node(np, dmtimer_match_table) {
		if (!dmtimer_is_preferred(np))
			continue;

		if (of_property_read_bool(np, "ti,timer-alwon")) {
			const __be32 *addr;

			addr = of_get_address(np, 0, NULL, NULL);
			pa = of_translate_address(np, addr);
			if (pa) {
				/* Quirky omap3 boards must use dmtimer12 */
				if (quirk_unreliable_oscillator &&
				    pa == 0x48318000)
					continue;

				of_node_put(np);
				break;
			}
		}
	}

	/* Usually no need for dmtimer clocksource if we have counter32 */
	if (counter_32k >= 0) {
		clockevent = pa;
		clocksource = 0;
	} else {
		clocksource = pa;
		clockevent = DMTIMER_INST_DONT_CARE;
	}
}

/* Finds the first usable dmtimer, used for the don't care case */
static u32 __init dmtimer_systimer_find_first_available(void)
{
	struct device_node *np;
	const __be32 *addr;
	u32 pa = 0;

	for_each_matching_node(np, dmtimer_match_table) {
		if (!dmtimer_is_preferred(np))
			continue;

		addr = of_get_address(np, 0, NULL, NULL);
		pa = of_translate_address(np, addr);
		if (pa) {
			if (pa == clocksource || pa == clockevent) {
				pa = 0;
				continue;
			}

			of_node_put(np);
			break;
		}
	}

	return pa;
}

/* Selects the best clocksource and clockevent to use */
static void __init dmtimer_systimer_select_best(void)
{
	dmtimer_systimer_check_counter32k();
	dmtimer_systimer_assign_alwon();

	if (clockevent == DMTIMER_INST_DONT_CARE)
		clockevent = dmtimer_systimer_find_first_available();

	pr_debug("%s: counter_32k: %i clocksource: %08x clockevent: %08x\n",
		 __func__, counter_32k, clocksource, clockevent);
}

/* Interface clocks are only available on some SoCs variants */
static int __init dmtimer_systimer_init_clock(struct dmtimer_systimer *t,
					      struct device_node *np,
					      const char *name,
					      unsigned long *rate)
{
	struct clk *clock;
	unsigned long r;
	bool is_ick = false;
	int error;

	is_ick = !strncmp(name, "ick", 3);

	clock = of_clk_get_by_name(np, name);
	if ((PTR_ERR(clock) == -EINVAL) && is_ick)
		return 0;
	else if (IS_ERR(clock))
		return PTR_ERR(clock);

	error = clk_prepare_enable(clock);
	if (error)
		return error;

	r = clk_get_rate(clock);
	if (!r)
		return -ENODEV;

	if (is_ick)
		t->ick = clock;
	else
		t->fck = clock;

	*rate = r;

	return 0;
}

static int __init dmtimer_systimer_setup(struct device_node *np,
					 struct dmtimer_systimer *t)
{
	unsigned long rate;
	u8 regbase;
	int error;

	if (!of_device_is_compatible(np->parent, "ti,sysc"))
		return -EINVAL;

	t->base = of_iomap(np, 0);
	if (!t->base)
		return -ENXIO;

	/*
	 * Enable optional assigned-clock-parents configured at the timer
	 * node level. For regular device drivers, this is done automatically
	 * by bus related code such as platform_drv_probe().
	 */
	error = of_clk_set_defaults(np, false);
	if (error < 0)
		pr_err("%s: clock source init failed: %i\n", __func__, error);

	/* For ti-sysc, we have timer clocks at the parent module level */
	error = dmtimer_systimer_init_clock(t, np->parent, "fck", &rate);
	if (error)
		goto err_unmap;

	t->rate = rate;

	error = dmtimer_systimer_init_clock(t, np->parent, "ick", &rate);
	if (error)
		goto err_unmap;

	if (dmtimer_systimer_revision1(t)) {
		t->irq_stat = OMAP_TIMER_V1_STAT_OFFSET;
		t->irq_ena = OMAP_TIMER_V1_INT_EN_OFFSET;
		t->pend = _OMAP_TIMER_WRITE_PEND_OFFSET;
		regbase = 0;
	} else {
		t->irq_stat = OMAP_TIMER_V2_IRQSTATUS;
		t->irq_ena = OMAP_TIMER_V2_IRQENABLE_SET;
		regbase = OMAP_TIMER_V2_FUNC_OFFSET;
		t->pend = regbase + _OMAP_TIMER_WRITE_PEND_OFFSET;
	}

	t->sysc = OMAP_TIMER_OCP_CFG_OFFSET;
	t->load = regbase + _OMAP_TIMER_LOAD_OFFSET;
	t->counter = regbase + _OMAP_TIMER_COUNTER_OFFSET;
	t->ctrl = regbase + _OMAP_TIMER_CTRL_OFFSET;
	t->wakeup = regbase + _OMAP_TIMER_WAKEUP_EN_OFFSET;
	t->ifctrl = regbase + _OMAP_TIMER_IF_CTRL_OFFSET;

	dmtimer_systimer_reset(t);
	dmtimer_systimer_enable(t);
	pr_debug("dmtimer rev %08x sysc %08x\n", readl_relaxed(t->base),
		 readl_relaxed(t->base + t->sysc));

	return 0;

err_unmap:
	iounmap(t->base);

	return error;
}

/* Clockevent */
static struct dmtimer_clockevent *
to_dmtimer_clockevent(struct clock_event_device *clockevent)
{
	return container_of(clockevent, struct dmtimer_clockevent, dev);
}

static irqreturn_t dmtimer_clockevent_interrupt(int irq, void *data)
{
	struct dmtimer_clockevent *clkevt = data;
	struct dmtimer_systimer *t = &clkevt->t;

	writel_relaxed(OMAP_TIMER_INT_OVERFLOW, t->base + t->irq_stat);
	clkevt->dev.event_handler(&clkevt->dev);

	return IRQ_HANDLED;
}

static int dmtimer_set_next_event(unsigned long cycles,
				  struct clock_event_device *evt)
{
	struct dmtimer_clockevent *clkevt = to_dmtimer_clockevent(evt);
	struct dmtimer_systimer *t = &clkevt->t;
	void __iomem *pend = t->base + t->pend;

	writel_relaxed(0xffffffff - cycles, t->base + t->counter);
	while (readl_relaxed(pend) & WP_TCRR)
		cpu_relax();

	writel_relaxed(OMAP_TIMER_CTRL_ST, t->base + t->ctrl);
	while (readl_relaxed(pend) & WP_TCLR)
		cpu_relax();

	return 0;
}

static int dmtimer_clockevent_shutdown(struct clock_event_device *evt)
{
	struct dmtimer_clockevent *clkevt = to_dmtimer_clockevent(evt);
	struct dmtimer_systimer *t = &clkevt->t;
	void __iomem *ctrl = t->base + t->ctrl;
	u32 l;

	l = readl_relaxed(ctrl);
	if (l & OMAP_TIMER_CTRL_ST) {
		l &= ~BIT(0);
		writel_relaxed(l, ctrl);
		/* Flush posted write */
		l = readl_relaxed(ctrl);
		/*  Wait for functional clock period x 3.5 */
		udelay(3500000 / t->rate + 1);
	}
	writel_relaxed(OMAP_TIMER_INT_OVERFLOW, t->base + t->irq_stat);

	return 0;
}

static int dmtimer_set_periodic(struct clock_event_device *evt)
{
	struct dmtimer_clockevent *clkevt = to_dmtimer_clockevent(evt);
	struct dmtimer_systimer *t = &clkevt->t;
	void __iomem *pend = t->base + t->pend;

	dmtimer_clockevent_shutdown(evt);

	/* Looks like we need to first set the load value separately */
	writel_relaxed(clkevt->period, t->base + t->load);
	while (readl_relaxed(pend) & WP_TLDR)
		cpu_relax();

	writel_relaxed(clkevt->period, t->base + t->counter);
	while (readl_relaxed(pend) & WP_TCRR)
		cpu_relax();

	writel_relaxed(OMAP_TIMER_CTRL_AR | OMAP_TIMER_CTRL_ST,
		       t->base + t->ctrl);
	while (readl_relaxed(pend) & WP_TCLR)
		cpu_relax();

	return 0;
}

static void omap_clockevent_idle(struct clock_event_device *evt)
{
	struct dmtimer_clockevent *clkevt = to_dmtimer_clockevent(evt);
	struct dmtimer_systimer *t = &clkevt->t;

	dmtimer_systimer_disable(t);
	clk_disable(t->fck);
}

static void omap_clockevent_unidle(struct clock_event_device *evt)
{
	struct dmtimer_clockevent *clkevt = to_dmtimer_clockevent(evt);
	struct dmtimer_systimer *t = &clkevt->t;
	int error;

	error = clk_enable(t->fck);
	if (error)
		pr_err("could not enable timer fck on resume: %i\n", error);

	dmtimer_systimer_enable(t);
	writel_relaxed(OMAP_TIMER_INT_OVERFLOW, t->base + t->irq_ena);
	writel_relaxed(OMAP_TIMER_INT_OVERFLOW, t->base + t->wakeup);
}

static int __init dmtimer_clockevent_init(struct device_node *np)
{
	struct dmtimer_clockevent *clkevt;
	struct clock_event_device *dev;
	struct dmtimer_systimer *t;
	int error;

	clkevt = kzalloc(sizeof(*clkevt), GFP_KERNEL);
	if (!clkevt)
		return -ENOMEM;

	t = &clkevt->t;
	dev = &clkevt->dev;

	/*
	 * We mostly use cpuidle_coupled with ARM local timers for runtime,
	 * so there's probably no use for CLOCK_EVT_FEAT_DYNIRQ here.
	 */
	dev->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
	dev->rating = 300;
	dev->set_next_event = dmtimer_set_next_event;
	dev->set_state_shutdown = dmtimer_clockevent_shutdown;
	dev->set_state_periodic = dmtimer_set_periodic;
	dev->set_state_oneshot = dmtimer_clockevent_shutdown;
	dev->tick_resume = dmtimer_clockevent_shutdown;
	dev->cpumask = cpu_possible_mask;

	dev->irq = irq_of_parse_and_map(np, 0);
	if (!dev->irq) {
		error = -ENXIO;
		goto err_out_free;
	}

	error = dmtimer_systimer_setup(np, &clkevt->t);
	if (error)
		goto err_out_free;

	clkevt->period = 0xffffffff - DIV_ROUND_CLOSEST(t->rate, HZ);

	/*
	 * For clock-event timers we never read the timer counter and
	 * so we are not impacted by errata i103 and i767. Therefore,
	 * we can safely ignore this errata for clock-event timers.
	 */
	writel_relaxed(OMAP_TIMER_CTRL_POSTED, t->base + t->ifctrl);

	error = request_irq(dev->irq, dmtimer_clockevent_interrupt,
			    IRQF_TIMER, "clockevent", clkevt);
	if (error)
		goto err_out_unmap;

	writel_relaxed(OMAP_TIMER_INT_OVERFLOW, t->base + t->irq_ena);
	writel_relaxed(OMAP_TIMER_INT_OVERFLOW, t->base + t->wakeup);

	pr_info("TI gptimer clockevent: %s%lu Hz at %pOF\n",
		of_find_property(np, "ti,timer-alwon", NULL) ?
		"always-on " : "", t->rate, np->parent);

	clockevents_config_and_register(dev, t->rate,
					3, /* Timer internal resynch latency */
					0xffffffff);

	if (of_machine_is_compatible("ti,am33xx") ||
	    of_machine_is_compatible("ti,am43")) {
		dev->suspend = omap_clockevent_idle;
		dev->resume = omap_clockevent_unidle;
	}

	return 0;

err_out_unmap:
	iounmap(t->base);

err_out_free:
	kfree(clkevt);

	return error;
}

/* Clocksource */
static struct dmtimer_clocksource *
to_dmtimer_clocksource(struct clocksource *cs)
{
	return container_of(cs, struct dmtimer_clocksource, dev);
}

static u64 dmtimer_clocksource_read_cycles(struct clocksource *cs)
{
	struct dmtimer_clocksource *clksrc = to_dmtimer_clocksource(cs);
	struct dmtimer_systimer *t = &clksrc->t;

	return (u64)readl_relaxed(t->base + t->counter);
}

static void __iomem *dmtimer_sched_clock_counter;

static u64 notrace dmtimer_read_sched_clock(void)
{
	return readl_relaxed(dmtimer_sched_clock_counter);
}

static void dmtimer_clocksource_suspend(struct clocksource *cs)
{
	struct dmtimer_clocksource *clksrc = to_dmtimer_clocksource(cs);
	struct dmtimer_systimer *t = &clksrc->t;

	clksrc->loadval = readl_relaxed(t->base + t->counter);
	dmtimer_systimer_disable(t);
	clk_disable(t->fck);
}

static void dmtimer_clocksource_resume(struct clocksource *cs)
{
	struct dmtimer_clocksource *clksrc = to_dmtimer_clocksource(cs);
	struct dmtimer_systimer *t = &clksrc->t;
	int error;

	error = clk_enable(t->fck);
	if (error)
		pr_err("could not enable timer fck on resume: %i\n", error);

	dmtimer_systimer_enable(t);
	writel_relaxed(clksrc->loadval, t->base + t->counter);
	writel_relaxed(OMAP_TIMER_CTRL_ST | OMAP_TIMER_CTRL_AR,
		       t->base + t->ctrl);
}

static int __init dmtimer_clocksource_init(struct device_node *np)
{
	struct dmtimer_clocksource *clksrc;
	struct dmtimer_systimer *t;
	struct clocksource *dev;
	int error;

	clksrc = kzalloc(sizeof(*clksrc), GFP_KERNEL);
	if (!clksrc)
		return -ENOMEM;

	dev = &clksrc->dev;
	t = &clksrc->t;

	error = dmtimer_systimer_setup(np, t);
	if (error)
		goto err_out_free;

	dev->name = "dmtimer";
	dev->rating = 300;
	dev->read = dmtimer_clocksource_read_cycles;
	dev->mask = CLOCKSOURCE_MASK(32);
	dev->flags = CLOCK_SOURCE_IS_CONTINUOUS;

	/* Unlike for clockevent, legacy code sets suspend only for am4 */
	if (of_machine_is_compatible("ti,am43")) {
		dev->suspend = dmtimer_clocksource_suspend;
		dev->resume = dmtimer_clocksource_resume;
	}

	writel_relaxed(0, t->base + t->counter);
	writel_relaxed(OMAP_TIMER_CTRL_ST | OMAP_TIMER_CTRL_AR,
		       t->base + t->ctrl);

	pr_info("TI gptimer clocksource: %s%pOF\n",
		of_find_property(np, "ti,timer-alwon", NULL) ?
		"always-on " : "", np->parent);

	if (!dmtimer_sched_clock_counter) {
		dmtimer_sched_clock_counter = t->base + t->counter;
		sched_clock_register(dmtimer_read_sched_clock, 32, t->rate);
	}

	if (clocksource_register_hz(dev, t->rate))
		pr_err("Could not register clocksource %pOF\n", np);

	return 0;

err_out_free:
	kfree(clksrc);

	return -ENODEV;
}

/*
 * To detect between a clocksource and clockevent, we assume the device tree
 * has no interrupts configured for a clocksource timer.
 */
static int __init dmtimer_systimer_init(struct device_node *np)
{
	const __be32 *addr;
	u32 pa;

	/* One time init for the preferred timer configuration */
	if (!clocksource && !clockevent)
		dmtimer_systimer_select_best();

	if (!clocksource && !clockevent) {
		pr_err("%s: unable to detect system timers, update dtb?\n",
		       __func__);

		return -EINVAL;
	}

	addr = of_get_address(np, 0, NULL, NULL);
	pa = of_translate_address(np, addr);
	if (!pa)
		return -EINVAL;

	if (counter_32k <= 0 && clocksource == pa)
		return dmtimer_clocksource_init(np);

	if (clockevent == pa)
		return dmtimer_clockevent_init(np);

	return 0;
}

TIMER_OF_DECLARE(systimer_omap2, "ti,omap2420-timer", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_omap3, "ti,omap3430-timer", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_omap4, "ti,omap4430-timer", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_omap5, "ti,omap5430-timer", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_am33x, "ti,am335x-timer", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_am3ms, "ti,am335x-timer-1ms", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_dm814, "ti,dm814-timer", dmtimer_systimer_init);
TIMER_OF_DECLARE(systimer_dm816, "ti,dm816-timer", dmtimer_systimer_init);