clocksource: timer-keystone: introduce clocksource driver for Keystone

Add broadcast clock-event device for the Keystone arch.

The timer can be configured as a general-purpose 64-bit timer,
dual general-purpose 32-bit timers. When configured as dual 32-bit
timers, each half can operate in conjunction (chain mode) or
independently (unchained mode) of each other.

Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Santosh shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Makefile

@@ -38,3 +38,4 @@ obj-$(CONFIG_ARM_ARCH_TIMER)		+= arm_arch_timer.o
 obj-$(CONFIG_ARM_GLOBAL_TIMER)		+= arm_global_timer.o
 obj-$(CONFIG_CLKSRC_METAG_GENERIC)	+= metag_generic.o
 obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST)	+= dummy_timer.o
+obj-$(CONFIG_ARCH_KEYSTONE)		+= timer-keystone.o

drivers/clocksource/timer-keystone.c

@@ -0,0 +1,244 @@
+/*
+ * Keystone broadcast clock-event
+ *
+ * Copyright 2013 Texas Instruments, Inc.
+ *
+ * Author: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/interrupt.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+
+#define TIMER_NAME			"timer-keystone"
+
+/* Timer register offsets */
+#define TIM12				0x10
+#define TIM34				0x14
+#define PRD12				0x18
+#define PRD34				0x1c
+#define TCR				0x20
+#define TGCR				0x24
+#define INTCTLSTAT			0x44
+
+/* Timer register bitfields */
+#define TCR_ENAMODE_MASK		0xC0
+#define TCR_ENAMODE_ONESHOT_MASK	0x40
+#define TCR_ENAMODE_PERIODIC_MASK	0x80
+
+#define TGCR_TIM_UNRESET_MASK		0x03
+#define INTCTLSTAT_ENINT_MASK		0x01
+
+/**
+ * struct keystone_timer: holds timer's data
+ * @base: timer memory base address
+ * @hz_period: cycles per HZ period
+ * @event_dev: event device based on timer
+ */
+static struct keystone_timer {
+	void __iomem *base;
+	unsigned long hz_period;
+	struct clock_event_device event_dev;
+} timer;
+
+static inline u32 keystone_timer_readl(unsigned long rg)
+{
+	return readl_relaxed(timer.base + rg);
+}
+
+static inline void keystone_timer_writel(u32 val, unsigned long rg)
+{
+	writel_relaxed(val, timer.base + rg);
+}
+
+/**
+ * keystone_timer_barrier: write memory barrier
+ * use explicit barrier to avoid using readl/writel non relaxed function
+ * variants, because in our case non relaxed variants hide the true places
+ * where barrier is needed.
+ */
+static inline void keystone_timer_barrier(void)
+{
+	__iowmb();
+}
+
+/**
+ * keystone_timer_config: configures timer to work in oneshot/periodic modes.
+ * @ mode: mode to configure
+ * @ period: cycles number to configure for
+ */
+static int keystone_timer_config(u64 period, enum clock_event_mode mode)
+{
+	u32 tcr;
+	u32 off;
+
+	tcr = keystone_timer_readl(TCR);
+	off = tcr & ~(TCR_ENAMODE_MASK);
+
+	/* set enable mode */
+	switch (mode) {
+	case CLOCK_EVT_MODE_ONESHOT:
+		tcr |= TCR_ENAMODE_ONESHOT_MASK;
+		break;
+	case CLOCK_EVT_MODE_PERIODIC:
+		tcr |= TCR_ENAMODE_PERIODIC_MASK;
+		break;
+	default:
+		return -1;
+	}
+
+	/* disable timer */
+	keystone_timer_writel(off, TCR);
+	/* here we have to be sure the timer has been disabled */
+	keystone_timer_barrier();
+
+	/* reset counter to zero, set new period */
+	keystone_timer_writel(0, TIM12);
+	keystone_timer_writel(0, TIM34);
+	keystone_timer_writel(period & 0xffffffff, PRD12);
+	keystone_timer_writel(period >> 32, PRD34);
+
+	/*
+	 * enable timer
+	 * here we have to be sure that CNTLO, CNTHI, PRDLO, PRDHI registers
+	 * have been written.
+	 */
+	keystone_timer_barrier();
+	keystone_timer_writel(tcr, TCR);
+	return 0;
+}
+
+static void keystone_timer_disable(void)
+{
+	u32 tcr;
+
+	tcr = keystone_timer_readl(TCR);
+
+	/* disable timer */
+	tcr &= ~(TCR_ENAMODE_MASK);
+	keystone_timer_writel(tcr, TCR);
+}
+
+static irqreturn_t keystone_timer_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = dev_id;
+
+	evt->event_handler(evt);
+	return IRQ_HANDLED;
+}
+
+static int keystone_set_next_event(unsigned long cycles,
+				  struct clock_event_device *evt)
+{
+	return keystone_timer_config(cycles, evt->mode);
+}
+
+static void keystone_set_mode(enum clock_event_mode mode,
+			     struct clock_event_device *evt)
+{
+	switch (mode) {
+	case CLOCK_EVT_MODE_PERIODIC:
+		keystone_timer_config(timer.hz_period, CLOCK_EVT_MODE_PERIODIC);
+		break;
+	case CLOCK_EVT_MODE_UNUSED:
+	case CLOCK_EVT_MODE_SHUTDOWN:
+	case CLOCK_EVT_MODE_ONESHOT:
+		keystone_timer_disable();
+		break;
+	default:
+		break;
+	}
+}
+
+static void __init keystone_timer_init(struct device_node *np)
+{
+	struct clock_event_device *event_dev = &timer.event_dev;
+	unsigned long rate;
+	struct clk *clk;
+	int irq, error;
+	u32 tgcr;
+
+	irq  = irq_of_parse_and_map(np, 0);
+	if (irq == NO_IRQ) {
+		pr_err("%s: failed to map interrupts\n", __func__);
+		return;
+	}
+
+	timer.base = of_iomap(np, 0);
+	if (!timer.base) {
+		pr_err("%s: failed to map registers\n", __func__);
+		return;
+	}
+
+	clk = of_clk_get(np, 0);
+	if (IS_ERR(clk)) {
+		pr_err("%s: failed to get clock\n", __func__);
+		iounmap(timer.base);
+		return;
+	}
+
+	error = clk_prepare_enable(clk);
+	if (error) {
+		pr_err("%s: failed to enable clock\n", __func__);
+		goto err;
+	}
+
+	rate = clk_get_rate(clk);
+
+	/* disable, use internal clock source */
+	keystone_timer_writel(0, TCR);
+	/* here we have to be sure the timer has been disabled */
+	keystone_timer_barrier();
+
+	/* reset timer as 64-bit, no pre-scaler, plus features are disabled */
+	tgcr = 0;
+	keystone_timer_writel(0, TGCR);
+
+	/* unreset timer */
+	tgcr |= TGCR_TIM_UNRESET_MASK;
+	keystone_timer_writel(tgcr, TGCR);
+
+	/* init counter to zero */
+	keystone_timer_writel(0, TIM12);
+	keystone_timer_writel(0, TIM34);
+
+	timer.hz_period = DIV_ROUND_UP(rate, HZ);
+
+	/* enable timer interrupts */
+	keystone_timer_writel(INTCTLSTAT_ENINT_MASK, INTCTLSTAT);
+
+	error = request_irq(irq, keystone_timer_interrupt, IRQF_TIMER,
+			    TIMER_NAME, event_dev);
+	if (error) {
+		pr_err("%s: failed to setup irq\n", __func__);
+		goto err;
+	}
+
+	/* setup clockevent */
+	event_dev->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
+	event_dev->set_next_event = keystone_set_next_event;
+	event_dev->set_mode = keystone_set_mode;
+	event_dev->cpumask = cpu_all_mask;
+	event_dev->owner = THIS_MODULE;
+	event_dev->name = TIMER_NAME;
+	event_dev->irq = irq;
+
+	clockevents_config_and_register(event_dev, rate, 1, ULONG_MAX);
+
+	pr_info("keystone timer clock @%lu Hz\n", rate);
+	return;
+err:
+	clk_put(clk);
+	iounmap(timer.base);
+}
+
+CLOCKSOURCE_OF_DECLARE(keystone_timer, "ti,keystone-timer",
+					keystone_timer_init);