[PATCH v2 02/11] clocksource:global_timer: Add ARM global timer support.

[Srinivas KANDAGATLA <srinivas.kandagatla@st.com>]

From: Stuart Menefy <stuart.menefy@st.com>

This is a simple driver for the global timer module found in the Cortex
A9-MP cores from revision r1p0 onwards. This should be able to perform
the functions of the system timer and the local timer in an SMP system.

The global timer has the following features:
    The global timer is a 64-bit incrementing counter with an
auto-incrementing feature. It continues incrementing after sending
interrupts. The global timer is memory mapped in the private memory
region.
    The global timer is accessible to all Cortex-A9 processors in the
cluster. Each Cortex-A9 processor has a private 64-bit comparator that
is used to assert a private interrupt when the global timer has reached
the comparator value. All the Cortex-A9 processors in a design use the
banked ID, ID27, for this interrupt. ID27 is sent to the Interrupt
Controller as a Private Peripheral Interrupt. The global timer is
clocked by PERIPHCLK.

Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
CC: Arnd Bergmann <arnd@arndb.de>
CC: Rob Herring <robherring2@gmail.com>
CC: Linus Walleij <linus.walleij@linaro.org>
CC: Will Deacon <will.deacon@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
---
 .../devicetree/bindings/arm/global_timer.txt       |   21 ++
 drivers/clocksource/Kconfig                        |   13 +
 drivers/clocksource/Makefile                       |    1 +
 drivers/clocksource/arm_global_timer.c             |  368 ++++++++++++++++++++
 4 files changed, 403 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/arm/global_timer.txt
 create mode 100644 drivers/clocksource/arm_global_timer.c

diff --git a/Documentation/devicetree/bindings/arm/global_timer.txt b/Documentation/devicetree/bindings/arm/global_timer.txt
new file mode 100644
index 0000000..b64abac
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/global_timer.txt
@@ -0,0 +1,21 @@
+
+* ARM Global Timer
+	Cortex-A9 are often associated with a per-core Global timer.
+
+** Timer node required properties:
+
+- compatible : Should be "arm,cortex-a9-global-timer"
+		Driver supports versions r2p0 and above.
+
+- interrupts : One interrupt to each core
+
+- reg : Specify the base address and the size of the GT timer
+	register window.
+
+Example:
+
+	timer@2c000600 {
+		compatible = "arm,cortex-a9-global-timer";
+		reg = <0x2c000600 0x20>;
+		interrupts = <1 13 0xf01>;
+	};
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index f151c6c..b0c4c42 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -67,6 +67,19 @@ config ARM_ARCH_TIMER
 	bool
 	select CLKSRC_OF if OF
 
+config ARM_GLOBAL_TIMER
+	bool
+	select CLKSRC_OF if OF
+	help
+	  This options enables support for the ARM global timer unit
+
+config CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
+	bool
+	depends on ARM_GLOBAL_TIMER
+	default y
+	help
+	 Use ARM global timer clock source as sched_clock
+
 config CLKSRC_METAG_GENERIC
 	def_bool y if METAG
 	help
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 8d979c7..b2363cb 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -28,4 +28,5 @@ obj-$(CONFIG_CLKSRC_EXYNOS_MCT)	+= exynos_mct.o
 obj-$(CONFIG_CLKSRC_SAMSUNG_PWM)	+= samsung_pwm_timer.o
 
 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
diff --git a/drivers/clocksource/arm_global_timer.c b/drivers/clocksource/arm_global_timer.c
new file mode 100644
index 0000000..e4bc4fe
--- /dev/null
+++ b/drivers/clocksource/arm_global_timer.c
@@ -0,0 +1,368 @@
+/*
+ * drivers/clocksource/arm_global_timer.c
+ *
+ * Copyright (C) 2013 STMicroelectronics (R&D) Limited.
+ * Author: Stuart Menefy <stuart.menefy@st.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/init.h>
+#include <linux/interrupt.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/clk.h>
+#include <linux/clkdev.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+
+#include <asm/sched_clock.h>
+#include <asm/mach/irq.h>
+#include <asm/cputype.h>
+#include <asm/localtimer.h>
+
+#define GT_COUNTER0	0x00
+#define GT_COUNTER1	0x04
+
+#define GT_CONTROL	0x08
+#define GT_CONTROL_TIMER_ENABLE		BIT(0)  /* this bit is NOT banked */
+#define GT_CONTROL_COMP_ENABLE		BIT(1)	/* banked */
+#define GT_CONTROL_IRQ_ENABLE		BIT(2)	/* banked */
+#define GT_CONTROL_AUTO_INC		BIT(3)	/* banked */
+
+#define GT_INT_STATUS	0x0c
+#define GT_INT_STATUS_EVENT_FLAG	BIT(0)
+
+#define GT_COMP0	0x10
+#define GT_COMP1	0x14
+#define GT_AUTO_INC	0x18
+
+/*
+ * We are expecting to be clocked by the ARM peripheral clock.
+ *
+ * Note: it is assumed we are using a prescaler value of zero, so this is
+ * the units for all operations.
+ */
+static void __iomem *gt_base;
+static unsigned long gt_clk_rate;
+static int gt_ppi;
+static struct clock_event_device __percpu **gt_evt;
+static DEFINE_PER_CPU(bool, percpu_init_called);
+static DEFINE_PER_CPU(struct clock_event_device, gt_clockevent);
+
+/*
+ * To get the value from the Global Timer Counter register proceed as follows:
+ * 1. Read the upper 32-bit timer counter register
+ * 2. Read the lower 32-bit timer counter register
+ * 3. Read the upper 32-bit timer counter register again. If the value is
+ *  different to the 32-bit upper value read previously, go back to step 2.
+ *  Otherwise the 64-bit timer counter value is correct.
+ */
+static u64 gt_counter_read(void)
+{
+	u64 counter;
+	u32 lower;
+	u32 upper, old_upper;
+
+	upper = __raw_readl(gt_base + GT_COUNTER1);
+	do {
+		old_upper = upper;
+		lower = __raw_readl(gt_base + GT_COUNTER0);
+		upper = __raw_readl(gt_base + GT_COUNTER1);
+	} while (upper != old_upper);
+
+	counter = upper;
+	counter <<= 32;
+	counter |= lower;
+	return counter;
+}
+
+/**
+ * To ensure that updates to comparator value register do not set the
+ * Interrupt Status Register proceed as follows:
+ * 1. Clear the Comp Enable bit in the Timer Control Register.
+ * 2. Write the lower 32-bit Comparator Value Register.
+ * 3. Write the upper 32-bit Comparator Value Register.
+ * 4. Set the Comp Enable bit and, if necessary, the IRQ enable bit.
+ */
+static void gt_compare_set(unsigned long delta, int periodic)
+{
+	u64 counter = gt_counter_read();
+	unsigned long ctrl = __raw_readl(gt_base + GT_CONTROL);
+
+	counter += delta;
+	ctrl &=  ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE);
+
+	__raw_writel(ctrl, gt_base + GT_CONTROL);
+	__raw_writel(lower_32_bits(counter), gt_base + GT_COMP0);
+	__raw_writel(upper_32_bits(counter), gt_base + GT_COMP1);
+
+	if (periodic) {
+		__raw_writel(delta, gt_base + GT_AUTO_INC);
+		ctrl |= GT_CONTROL_AUTO_INC;
+	}
+
+	ctrl |= GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE;
+	__raw_writel(ctrl, gt_base + GT_CONTROL);
+}
+
+static void gt_clockevent_set_mode(enum clock_event_mode mode,
+				   struct clock_event_device *clk)
+{
+	unsigned long ctrl;
+
+	ctrl = __raw_readl(gt_base + GT_CONTROL);
+	switch (mode) {
+	case CLOCK_EVT_MODE_PERIODIC:
+		gt_compare_set(DIV_ROUND_CLOSEST(gt_clk_rate, HZ), 1);
+		break;
+	case CLOCK_EVT_MODE_ONESHOT:
+		ctrl &= ~(GT_CONTROL_AUTO_INC);
+		__raw_writel(ctrl, gt_base + GT_CONTROL);
+		break;
+	/* Can not shut down it as enable bit is not banked */
+	case CLOCK_EVT_MODE_UNUSED:
+	case CLOCK_EVT_MODE_SHUTDOWN:
+		ctrl &= ~(GT_CONTROL_COMP_ENABLE |
+				GT_CONTROL_IRQ_ENABLE | GT_CONTROL_AUTO_INC);
+		__raw_writel(ctrl, gt_base + GT_CONTROL);
+		break;
+	default:
+		break;
+	}
+}
+
+static int gt_clockevent_set_next_event(unsigned long evt,
+					struct clock_event_device *unused)
+{
+	gt_compare_set(evt, 0);
+	return 0;
+}
+
+static irqreturn_t gt_clockevent_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = *(struct clock_event_device **)dev_id;
+
+	if (__raw_readl(gt_base + GT_INT_STATUS) & GT_INT_STATUS_EVENT_FLAG) {
+		/**
+		 * ERRATA 740657( Global Timer can send 2 interrupts for
+		 * the same event in single-shot mode)
+		 * Workaround:
+		 *	Either disable single-shot mode.
+		 *	Or
+		 *	Modify the Interrupt Handler to avoid the
+		 *	offending sequence. This is achieved by clearing
+		 *	the Global Timer flag _after_ having incremented
+		 *	the Comparator register	value to a higher value.
+		 */
+		if (!(__raw_readl(gt_base + GT_CONTROL) & GT_CONTROL_AUTO_INC))
+			gt_compare_set(ULONG_MAX, 0);
+
+		__raw_writel(GT_INT_STATUS_EVENT_FLAG, gt_base + GT_INT_STATUS);
+
+		evt->event_handler(evt);
+		return IRQ_HANDLED;
+	}
+
+	return IRQ_NONE;
+}
+
+static int __cpuinit gt_clockevents_init(struct clock_event_device *clk)
+{
+	struct clock_event_device **this_cpu_clk;
+	int cpu = smp_processor_id();
+
+	clk->name = "ARM global timer clock event";
+	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
+	clk->set_mode = gt_clockevent_set_mode;
+	clk->set_next_event = gt_clockevent_set_next_event;
+	this_cpu_clk = __this_cpu_ptr(gt_evt);
+	*this_cpu_clk = clk;
+	clk->cpumask = cpumask_of(cpu);
+	clk->irq = gt_ppi;
+	clockevents_config_and_register(clk, gt_clk_rate,
+					0, 0xffffffff);
+	per_cpu(percpu_init_called, cpu) = true;
+	enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
+	return 0;
+}
+
+static void gt_clockevents_stop(struct clock_event_device *clk)
+{
+	gt_clockevent_set_mode(CLOCK_EVT_MODE_UNUSED, clk);
+	disable_percpu_irq(clk->irq);
+}
+
+static int __cpuinit gt_clockevents_setup(struct clock_event_device *clk)
+{
+	/* Use existing clock_event for boot cpu */
+	if (per_cpu(percpu_init_called, smp_processor_id()))
+		return 0;
+
+	/* already enabled in gt_clocksource_init. */
+	return gt_clockevents_init(clk);
+}
+
+static cycle_t gt_clocksource_read(struct clocksource *cs)
+{
+	return gt_counter_read();
+}
+
+static struct clocksource gt_clocksource = {
+	.name	= "ARM global timer clock source",
+	.rating	= 300,
+	.read	= gt_clocksource_read,
+	.mask	= CLOCKSOURCE_MASK(64),
+	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+#ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
+static u32 gt_sched_clock_read(void)
+{
+	if (!gt_base)
+		return 0;
+
+	return gt_counter_read();
+}
+#endif
+
+static void __init gt_clocksource_init(void)
+{
+	__raw_writel(0, gt_base + GT_CONTROL);
+	__raw_writel(0, gt_base + GT_COUNTER0);
+	__raw_writel(0, gt_base + GT_COUNTER1);
+	/* enables timer on all the cores */
+	__raw_writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
+
+#ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
+	setup_sched_clock(gt_sched_clock_read, 32, gt_clk_rate);
+#endif
+	clocksource_register_hz(&gt_clocksource, gt_clk_rate);
+}
+
+static struct clk *gt_get_clock(void)
+{
+	struct clk *clk;
+	int err;
+
+	clk = clk_get_sys("gt", NULL);
+	if (IS_ERR(clk)) {
+		pr_err("global-timer: clock not found: %ld\n", PTR_ERR(clk));
+		return clk;
+	}
+
+	err = clk_prepare_enable(clk);
+	if (err) {
+		pr_err("global-timer: clock prepare+enable failed: %d\n", err);
+		clk_put(clk);
+		return ERR_PTR(err);
+	}
+
+	return clk;
+}
+
+static struct local_timer_ops gt_lt_ops __cpuinitdata = {
+	.setup	= gt_clockevents_setup,
+	.stop	= gt_clockevents_stop,
+};
+
+int __init global_timer_init(void __iomem *base, unsigned int timer_irq)
+{
+	unsigned int cpu = smp_processor_id();
+	struct clock_event_device *evt = &per_cpu(gt_clockevent, cpu);
+	int err = 0;
+	struct clk *gt_clk;
+
+	if (gt_base) {
+		pr_warn("global-timer: invalid base address\n");
+		return -EINVAL;
+	}
+
+	gt_clk = gt_get_clock();
+	if (IS_ERR(gt_clk)) {
+		pr_warn("global-timer: clk not found\n");
+		return -EINVAL;
+	}
+
+	gt_evt = alloc_percpu(struct clock_event_device *);
+	if (!gt_evt) {
+		pr_warn("global-timer: can't allocate memory\n");
+		return -ENOMEM;
+	}
+
+	err = request_percpu_irq(timer_irq, gt_clockevent_interrupt,
+				 "gt", gt_evt);
+	if (err) {
+		pr_warn("global-timer: can't register interrupt %d (%d)\n",
+			timer_irq, err);
+		goto out_free;
+	}
+
+	gt_base = base;
+	gt_clk_rate = clk_get_rate(gt_clk);
+	gt_ppi = timer_irq;
+	gt_clocksource_init();
+	gt_clockevents_init(evt);
+#ifdef CONFIG_LOCAL_TIMERS
+	err =  local_timer_register(&gt_lt_ops);
+	if (err) {
+		pr_warn("global-timer: unable to register local timer.\n");
+		goto out_irq;
+	}
+#endif
+	return 0;
+
+out_irq:
+	free_percpu_irq(timer_irq, gt_evt);
+out_free:
+	free_percpu(gt_evt);
+	return err;
+}
+
+#ifdef CONFIG_OF
+static void __init global_timer_of_register(struct device_node *np)
+{
+	struct clk *clk;
+	int err = 0;
+	int gt_ppi;
+	static void __iomem *gt_base;
+
+	/*
+	 * In r2p0 the comparators for each processor with the global timer
+	 * fire when the timer value is greater than or equal to. In previous
+	 * revisions the comparators fired when the timer value was equal to.
+	 */
+	if ((read_cpuid_id() & 0xf0000f) < 0x200000)
+		goto out;
+
+	gt_ppi = irq_of_parse_and_map(np, 0);
+	if (!gt_ppi) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	gt_base = of_iomap(np, 0);
+	if (!gt_base) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	clk = of_clk_get(np, 0);
+	if (!IS_ERR(clk))
+		clk_register_clkdev(clk, NULL, "gt");
+
+	global_timer_init(gt_base, gt_ppi);
+
+out:
+	WARN(err, "Global timer register failed (%d)\n", err);
+}
+
+/* Only tested on r2p2 and r3p0  */
+CLOCKSOURCE_OF_DECLARE(arm_gt, "arm,cortex-a9-global-timer",
+			global_timer_of_register);
+#endif
-- 
1.7.6.5