ARM: imx: Add EPIT support

The Enhanced Periodic Interrupt Timer (EPIT) is found on newer
i.MX SoCs and can be used as an alternative system timer.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/plat-mxc/Kconfig

@@ -92,6 +92,18 @@ config MXC_DEBUG_BOARD
 	  data/address de-multiplexing and decode, signal level shift,
 	  interrupt control and various board functions.
 
+config HAVE_EPIT
+	bool
+
+config MXC_USE_EPIT
+	bool "Use EPIT instead of GPT"
+	depends on HAVE_EPIT
+	help
+	  Use EPIT as the system timer on systems that have it. Normally you
+	  don't have a reason to do so as the EPIT has the same features and
+	  uses the same clocks as the GPT. Anyway, on some systems the GPT
+	  may be in use for other purposes.
+
 config MXC_ULPI
 	bool
 

arch/arm/plat-mxc/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_ARCH_MXC_IOMUX_V3) += iomux-v3.o
 obj-$(CONFIG_MXC_PWM)  += pwm.o
 obj-$(CONFIG_USB_EHCI_MXC) += ehci.o
 obj-$(CONFIG_MXC_ULPI) += ulpi.o
+obj-$(CONFIG_MXC_USE_EPIT) += epit.o
 obj-$(CONFIG_ARCH_MXC_AUDMUX_V1) += audmux-v1.o
 obj-$(CONFIG_ARCH_MXC_AUDMUX_V2) += audmux-v2.o
 obj-$(CONFIG_MXC_DEBUG_BOARD) += 3ds_debugboard.o

arch/arm/plat-mxc/epit.c

@@ -0,0 +1,242 @@
+/*
+ *  linux/arch/arm/plat-mxc/epit.c
+ *
+ *  Copyright (C) 2010 Sascha Hauer <s.hauer@pengutronix.de>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02110-1301, USA.
+ */
+
+#define EPITCR		0x00
+#define EPITSR		0x04
+#define EPITLR		0x08
+#define EPITCMPR	0x0c
+#define EPITCNR		0x10
+
+#define EPITCR_EN			(1 << 0)
+#define EPITCR_ENMOD			(1 << 1)
+#define EPITCR_OCIEN			(1 << 2)
+#define EPITCR_RLD			(1 << 3)
+#define EPITCR_PRESC(x)			(((x) & 0xfff) << 4)
+#define EPITCR_SWR			(1 << 16)
+#define EPITCR_IOVW			(1 << 17)
+#define EPITCR_DBGEN			(1 << 18)
+#define EPITCR_WAITEN			(1 << 19)
+#define EPITCR_RES			(1 << 20)
+#define EPITCR_STOPEN			(1 << 21)
+#define EPITCR_OM_DISCON		(0 << 22)
+#define EPITCR_OM_TOGGLE		(1 << 22)
+#define EPITCR_OM_CLEAR			(2 << 22)
+#define EPITCR_OM_SET			(3 << 22)
+#define EPITCR_CLKSRC_OFF		(0 << 24)
+#define EPITCR_CLKSRC_PERIPHERAL	(1 << 24)
+#define EPITCR_CLKSRC_REF_HIGH		(1 << 24)
+#define EPITCR_CLKSRC_REF_LOW		(3 << 24)
+
+#define EPITSR_OCIF			(1 << 0)
+
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/clockchips.h>
+#include <linux/clk.h>
+
+#include <mach/hardware.h>
+#include <asm/mach/time.h>
+#include <mach/common.h>
+
+static struct clock_event_device clockevent_epit;
+static enum clock_event_mode clockevent_mode = CLOCK_EVT_MODE_UNUSED;
+
+static void __iomem *timer_base;
+
+static inline void epit_irq_disable(void)
+{
+	u32 val;
+
+	val = __raw_readl(timer_base + EPITCR);
+	val &= ~EPITCR_OCIEN;
+	__raw_writel(val, timer_base + EPITCR);
+}
+
+static inline void epit_irq_enable(void)
+{
+	u32 val;
+
+	val = __raw_readl(timer_base + EPITCR);
+	val |= EPITCR_OCIEN;
+	__raw_writel(val, timer_base + EPITCR);
+}
+
+static void epit_irq_acknowledge(void)
+{
+	__raw_writel(EPITSR_OCIF, timer_base + EPITSR);
+}
+
+static cycle_t epit_read(struct clocksource *cs)
+{
+	return 0 - __raw_readl(timer_base + EPITCNR);
+}
+
+static struct clocksource clocksource_epit = {
+	.name		= "epit",
+	.rating		= 200,
+	.read		= epit_read,
+	.mask		= CLOCKSOURCE_MASK(32),
+	.shift		= 20,
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static int __init epit_clocksource_init(struct clk *timer_clk)
+{
+	unsigned int c = clk_get_rate(timer_clk);
+
+	clocksource_epit.mult = clocksource_hz2mult(c,
+					clocksource_epit.shift);
+	clocksource_register(&clocksource_epit);
+
+	return 0;
+}
+
+/* clock event */
+
+static int epit_set_next_event(unsigned long evt,
+			      struct clock_event_device *unused)
+{
+	unsigned long tcmp;
+
+	tcmp = __raw_readl(timer_base + EPITCNR);
+
+	__raw_writel(tcmp - evt, timer_base + EPITCMPR);
+
+	return 0;
+}
+
+static void epit_set_mode(enum clock_event_mode mode,
+				struct clock_event_device *evt)
+{
+	unsigned long flags;
+
+	/*
+	 * The timer interrupt generation is disabled at least
+	 * for enough time to call epit_set_next_event()
+	 */
+	local_irq_save(flags);
+
+	/* Disable interrupt in GPT module */
+	epit_irq_disable();
+
+	if (mode != clockevent_mode) {
+		/* Set event time into far-far future */
+
+		/* Clear pending interrupt */
+		epit_irq_acknowledge();
+	}
+
+	/* Remember timer mode */
+	clockevent_mode = mode;
+	local_irq_restore(flags);
+
+	switch (mode) {
+	case CLOCK_EVT_MODE_PERIODIC:
+		printk(KERN_ERR "epit_set_mode: Periodic mode is not "
+				"supported for i.MX EPIT\n");
+		break;
+	case CLOCK_EVT_MODE_ONESHOT:
+	/*
+	 * Do not put overhead of interrupt enable/disable into
+	 * epit_set_next_event(), the core has about 4 minutes
+	 * to call epit_set_next_event() or shutdown clock after
+	 * mode switching
+	 */
+		local_irq_save(flags);
+		epit_irq_enable();
+		local_irq_restore(flags);
+		break;
+	case CLOCK_EVT_MODE_SHUTDOWN:
+	case CLOCK_EVT_MODE_UNUSED:
+	case CLOCK_EVT_MODE_RESUME:
+		/* Left event sources disabled, no more interrupts appear */
+		break;
+	}
+}
+
+/*
+ * IRQ handler for the timer
+ */
+static irqreturn_t epit_timer_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = &clockevent_epit;
+
+	epit_irq_acknowledge();
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+static struct irqaction epit_timer_irq = {
+	.name		= "i.MX EPIT Timer Tick",
+	.flags		= IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
+	.handler	= epit_timer_interrupt,
+};
+
+static struct clock_event_device clockevent_epit = {
+	.name		= "epit",
+	.features	= CLOCK_EVT_FEAT_ONESHOT,
+	.shift		= 32,
+	.set_mode	= epit_set_mode,
+	.set_next_event	= epit_set_next_event,
+	.rating		= 200,
+};
+
+static int __init epit_clockevent_init(struct clk *timer_clk)
+{
+	unsigned int c = clk_get_rate(timer_clk);
+
+	clockevent_epit.mult = div_sc(c, NSEC_PER_SEC,
+					clockevent_epit.shift);
+	clockevent_epit.max_delta_ns =
+			clockevent_delta2ns(0xfffffffe, &clockevent_epit);
+	clockevent_epit.min_delta_ns =
+			clockevent_delta2ns(0x800, &clockevent_epit);
+
+	clockevent_epit.cpumask = cpumask_of(0);
+
+	clockevents_register_device(&clockevent_epit);
+
+	return 0;
+}
+
+void __init epit_timer_init(struct clk *timer_clk, void __iomem *base, int irq)
+{
+	clk_enable(timer_clk);
+
+	timer_base = base;
+
+	/*
+	 * Initialise to a known state (all timers off, and timing reset)
+	 */
+	__raw_writel(0x0, timer_base + EPITCR);
+
+	__raw_writel(0xffffffff, timer_base + EPITLR);
+	__raw_writel(EPITCR_EN | EPITCR_CLKSRC_REF_HIGH | EPITCR_WAITEN,
+			timer_base + EPITCR);
+
+	/* init and register the timer to the framework */
+	epit_clocksource_init(timer_clk);
+	epit_clockevent_init(timer_clk);
+
+	/* Make irqs happen */
+	setup_irq(irq, &epit_timer_irq);
+}

arch/arm/plat-mxc/include/mach/common.h

@@ -32,6 +32,7 @@ extern void mx31_init_irq(void);
 extern void mx35_init_irq(void);
 extern void mx51_init_irq(void);
 extern void mxc91231_init_irq(void);
+extern void epit_timer_init(struct clk *timer_clk, void __iomem *base, int irq);
 extern void mxc_timer_init(struct clk *timer_clk, void __iomem *, int);
 extern int mx1_clocks_init(unsigned long fref);
 extern int mx21_clocks_init(unsigned long lref, unsigned long fref);