1 files changed, 250 insertions, 0 deletions
diff --git a/drivers/clocksource/timer-atmel-st.c b/drivers/clocksource/timer-atmel-st.c
new file mode 100644
index 000000000..73e8aee44
--- /dev/null
+++ b/drivers/clocksource/timer-atmel-st.c
@@ -0,0 +1,250 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * linux/arch/arm/mach-at91/at91rm9200_time.c
+ *
+ *  Copyright (C) 2003 SAN People
+ *  Copyright (C) 2003 ATMEL
+ */
+
+#include <linux/kernel.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/export.h>
+#include <linux/mfd/syscon.h>
+#include <linux/mfd/syscon/atmel-st.h>
+#include <linux/of_irq.h>
+#include <linux/regmap.h>
+
+static unsigned long last_crtr;
+static u32 irqmask;
+static struct clock_event_device clkevt;
+static struct regmap *regmap_st;
+static int timer_latch;
+
+/*
+ * The ST_CRTR is updated asynchronously to the master clock ... but
+ * the updates as seen by the CPU don't seem to be strictly monotonic.
+ * Waiting until we read the same value twice avoids glitching.
+ */
+static inline unsigned long read_CRTR(void)
+{
+	unsigned int x1, x2;
+
+	regmap_read(regmap_st, AT91_ST_CRTR, &x1);
+	do {
+		regmap_read(regmap_st, AT91_ST_CRTR, &x2);
+		if (x1 == x2)
+			break;
+		x1 = x2;
+	} while (1);
+	return x1;
+}
+
+/*
+ * IRQ handler for the timer.
+ */
+static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
+{
+	u32 sr;
+
+	regmap_read(regmap_st, AT91_ST_SR, &sr);
+	sr &= irqmask;
+
+	/*
+	 * irqs should be disabled here, but as the irq is shared they are only
+	 * guaranteed to be off if the timer irq is registered first.
+	 */
+	WARN_ON_ONCE(!irqs_disabled());
+
+	/* simulate "oneshot" timer with alarm */
+	if (sr & AT91_ST_ALMS) {
+		clkevt.event_handler(&clkevt);
+		return IRQ_HANDLED;
+	}
+
+	/* periodic mode should handle delayed ticks */
+	if (sr & AT91_ST_PITS) {
+		u32	crtr = read_CRTR();
+
+		while (((crtr - last_crtr) & AT91_ST_CRTV) >= timer_latch) {
+			last_crtr += timer_latch;
+			clkevt.event_handler(&clkevt);
+		}
+		return IRQ_HANDLED;
+	}
+
+	/* this irq is shared ... */
+	return IRQ_NONE;
+}
+
+static u64 read_clk32k(struct clocksource *cs)
+{
+	return read_CRTR();
+}
+
+static struct clocksource clk32k = {
+	.name		= "32k_counter",
+	.rating		= 150,
+	.read		= read_clk32k,
+	.mask		= CLOCKSOURCE_MASK(20),
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static void clkdev32k_disable_and_flush_irq(void)
+{
+	unsigned int val;
+
+	/* Disable and flush pending timer interrupts */
+	regmap_write(regmap_st, AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
+	regmap_read(regmap_st, AT91_ST_SR, &val);
+	last_crtr = read_CRTR();
+}
+
+static int clkevt32k_shutdown(struct clock_event_device *evt)
+{
+	clkdev32k_disable_and_flush_irq();
+	irqmask = 0;
+	regmap_write(regmap_st, AT91_ST_IER, irqmask);
+	return 0;
+}
+
+static int clkevt32k_set_oneshot(struct clock_event_device *dev)
+{
+	clkdev32k_disable_and_flush_irq();
+
+	/*
+	 * ALM for oneshot irqs, set by next_event()
+	 * before 32 seconds have passed.
+	 */
+	irqmask = AT91_ST_ALMS;
+	regmap_write(regmap_st, AT91_ST_RTAR, last_crtr);
+	regmap_write(regmap_st, AT91_ST_IER, irqmask);
+	return 0;
+}
+
+static int clkevt32k_set_periodic(struct clock_event_device *dev)
+{
+	clkdev32k_disable_and_flush_irq();
+
+	/* PIT for periodic irqs; fixed rate of 1/HZ */
+	irqmask = AT91_ST_PITS;
+	regmap_write(regmap_st, AT91_ST_PIMR, timer_latch);
+	regmap_write(regmap_st, AT91_ST_IER, irqmask);
+	return 0;
+}
+
+static int
+clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
+{
+	u32		alm;
+	unsigned int	val;
+
+	BUG_ON(delta < 2);
+
+	/* The alarm IRQ uses absolute time (now+delta), not the relative
+	 * time (delta) in our calling convention.  Like all clockevents
+	 * using such "match" hardware, we have a race to defend against.
+	 *
+	 * Our defense here is to have set up the clockevent device so the
+	 * delta is at least two.  That way we never end up writing RTAR
+	 * with the value then held in CRTR ... which would mean the match
+	 * wouldn't trigger until 32 seconds later, after CRTR wraps.
+	 */
+	alm = read_CRTR();
+
+	/* Cancel any pending alarm; flush any pending IRQ */
+	regmap_write(regmap_st, AT91_ST_RTAR, alm);
+	regmap_read(regmap_st, AT91_ST_SR, &val);
+
+	/* Schedule alarm by writing RTAR. */
+	alm += delta;
+	regmap_write(regmap_st, AT91_ST_RTAR, alm);
+
+	return 0;
+}
+
+static struct clock_event_device clkevt = {
+	.name			= "at91_tick",
+	.features		= CLOCK_EVT_FEAT_PERIODIC |
+				  CLOCK_EVT_FEAT_ONESHOT,
+	.rating			= 150,
+	.set_next_event		= clkevt32k_next_event,
+	.set_state_shutdown	= clkevt32k_shutdown,
+	.set_state_periodic	= clkevt32k_set_periodic,
+	.set_state_oneshot	= clkevt32k_set_oneshot,
+	.tick_resume		= clkevt32k_shutdown,
+};
+
+/*
+ * ST (system timer) module supports both clockevents and clocksource.
+ */
+static int __init atmel_st_timer_init(struct device_node *node)
+{
+	struct clk *sclk;
+	unsigned int sclk_rate, val;
+	int irq, ret;
+
+	regmap_st = syscon_node_to_regmap(node);
+	if (IS_ERR(regmap_st)) {
+		pr_err("Unable to get regmap\n");
+		return PTR_ERR(regmap_st);
+	}
+
+	/* Disable all timer interrupts, and clear any pending ones */
+	regmap_write(regmap_st, AT91_ST_IDR,
+		AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
+	regmap_read(regmap_st, AT91_ST_SR, &val);
+
+	/* Get the interrupts property */
+	irq  = irq_of_parse_and_map(node, 0);
+	if (!irq) {
+		pr_err("Unable to get IRQ from DT\n");
+		return -EINVAL;
+	}
+
+	/* Make IRQs happen for the system timer */
+	ret = request_irq(irq, at91rm9200_timer_interrupt,
+			  IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
+			  "at91_tick", regmap_st);
+	if (ret) {
+		pr_err("Unable to setup IRQ\n");
+		return ret;
+	}
+
+	sclk = of_clk_get(node, 0);
+	if (IS_ERR(sclk)) {
+		pr_err("Unable to get slow clock\n");
+		return PTR_ERR(sclk);
+	}
+
+	ret = clk_prepare_enable(sclk);
+	if (ret) {
+		pr_err("Could not enable slow clock\n");
+		return ret;
+	}
+
+	sclk_rate = clk_get_rate(sclk);
+	if (!sclk_rate) {
+		pr_err("Invalid slow clock rate\n");
+		return -EINVAL;
+	}
+	timer_latch = (sclk_rate + HZ / 2) / HZ;
+
+	/* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
+	 * directly for the clocksource and all clockevents, after adjusting
+	 * its prescaler from the 1 Hz default.
+	 */
+	regmap_write(regmap_st, AT91_ST_RTMR, 1);
+
+	/* Setup timer clockevent, with minimum of two ticks (important!!) */
+	clkevt.cpumask = cpumask_of(0);
+	clockevents_config_and_register(&clkevt, sclk_rate,
+					2, AT91_ST_ALMV);
+
+	/* register clocksource */
+	return clocksource_register_hz(&clk32k, sclk_rate);
+}
+TIMER_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st",
+		       atmel_st_timer_init);