[ARM] 4811/1: RealView: clocksource support for the RealView platforms

The patch updates the RealView platform code to use the generic
clocksource infrastructure for basic time keeping. Based on the
Versatile implementation by Kevin Hilman.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig

@@ -168,6 +168,7 @@ config ARCH_REALVIEW
 	bool "ARM Ltd. RealView family"
 	select ARM_AMBA
 	select ICST307
+	select GENERIC_TIME
 	help
 	  This enables support for ARM Ltd RealView boards.
 

arch/arm/mach-realview/core.c

@@ -25,6 +25,7 @@
 #include <linux/interrupt.h>
 #include <linux/amba/bus.h>
 #include <linux/amba/clcd.h>
+#include <linux/clocksource.h>
 
 #include <asm/system.h>
 #include <asm/hardware.h>
@@ -484,47 +485,6 @@ void realview_leds_event(led_event_t ledevt)
 #define TICKS2USECS(x)	((x) / TICKS_PER_uSEC)
 #endif
 
-/*
- * Returns number of ms since last clock interrupt.  Note that interrupts
- * will have been disabled by do_gettimeoffset()
- */
-static unsigned long realview_gettimeoffset(void)
-{
-	unsigned long ticks1, ticks2, status;
-
-	/*
-	 * Get the current number of ticks.  Note that there is a race
-	 * condition between us reading the timer and checking for
-	 * an interrupt.  We get around this by ensuring that the
-	 * counter has not reloaded between our two reads.
-	 */
-	ticks2 = readl(TIMER0_VA_BASE + TIMER_VALUE) & 0xffff;
-	do {
-		ticks1 = ticks2;
-		status = __raw_readl(__io_address(REALVIEW_GIC_DIST_BASE + GIC_DIST_PENDING_SET)
-				     + ((IRQ_TIMERINT0_1 >> 5) << 2));
-		ticks2 = readl(TIMER0_VA_BASE + TIMER_VALUE) & 0xffff;
-	} while (ticks2 > ticks1);
-
-	/*
-	 * Number of ticks since last interrupt.
-	 */
-	ticks1 = TIMER_RELOAD - ticks2;
-
-	/*
-	 * Interrupt pending?  If so, we've reloaded once already.
-	 *
-	 * FIXME: Need to check this is effectively timer 0 that expires
-	 */
-	if (status & IRQMASK_TIMERINT0_1)
-		ticks1 += TIMER_RELOAD;
-
-	/*
-	 * Convert the ticks to usecs
-	 */
-	return TICKS2USECS(ticks1);
-}
-
 /*
  * IRQ handler for the timer
  */
@@ -549,6 +509,34 @@ static struct irqaction realview_timer_irq = {
 	.handler	= realview_timer_interrupt,
 };
 
+static cycle_t realview_get_cycles(void)
+{
+	return ~readl(TIMER3_VA_BASE + TIMER_VALUE);
+}
+
+static struct clocksource clocksource_realview = {
+	.name	= "timer3",
+	.rating	= 200,
+	.read	= realview_get_cycles,
+	.mask	= CLOCKSOURCE_MASK(32),
+	.shift	= 20,
+	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static void __init realview_clocksource_init(void)
+{
+	/* setup timer 0 as free-running clocksource */
+	writel(0, TIMER3_VA_BASE + TIMER_CTRL);
+	writel(0xffffffff, TIMER3_VA_BASE + TIMER_LOAD);
+	writel(0xffffffff, TIMER3_VA_BASE + TIMER_VALUE);
+	writel(TIMER_CTRL_32BIT | TIMER_CTRL_ENABLE | TIMER_CTRL_PERIODIC,
+		TIMER3_VA_BASE + TIMER_CTRL);
+
+	clocksource_realview.mult =
+		clocksource_khz2mult(1000, clocksource_realview.shift);
+	clocksource_register(&clocksource_realview);
+}
+
 /*
  * Set up timer interrupt, and return the current time in seconds.
  */
@@ -585,9 +573,10 @@ static void __init realview_timer_init(void)
 	 * Make irqs happen for the system timer
 	 */
 	setup_irq(IRQ_TIMERINT0_1, &realview_timer_irq);
+
+	realview_clocksource_init();
 }
 
 struct sys_timer realview_timer = {
 	.init		= realview_timer_init,
-	.offset		= realview_gettimeoffset,
 };