ARM: ks8695: convert to generic time and clocksource

Old platforms using ancient gettimeoffset() and other arcane
APIs are standing in the way of cleaning up the ARM kernel.
The gettimeoffset() was also broken: it would try to read out
the timer counter value, while this would not work (the
counter statically returns the initially programmed value)
so the implementation would anyway fall back to a homebrew
version of jiffie calculation.

This is an attempt at blind-coding a generic time and clocksource
driver for the platform by way of a datasheet and looking at the
old code.

Tested-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

arch/arm/Kconfig

@@ -652,8 +652,9 @@ config ARCH_KS8695
 	bool "Micrel/Kendin KS8695"
 	select CPU_ARM922T
 	select ARCH_REQUIRE_GPIOLIB
-	select ARCH_USES_GETTIMEOFFSET
 	select NEED_MACH_MEMORY_H
+	select CLKSRC_MMIO
+	select GENERIC_CLOCKEVENTS
 	help
 	  Support for Micrel/Kendin KS8695 "Centaur" (ARM922T) based
 	  System-on-Chip devices.

arch/arm/mach-ks8695/time.c

@@ -25,6 +25,7 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/io.h>
+#include <linux/clockchips.h>
 
 #include <asm/mach/time.h>
 #include <asm/system_misc.h>
@@ -53,44 +54,69 @@
 /* Timer0 Timeout Counter Register */
 #define T0TC_WATCHDOG		(0xff)		/* Enable watchdog mode */
 
-/*
- * Returns number of ms since last clock interrupt.  Note that interrupts
- * will have been disabled by do_gettimeoffset()
- */
-static unsigned long ks8695_gettimeoffset (void)
+static void ks8695_set_mode(enum clock_event_mode mode,
+			    struct clock_event_device *evt)
 {
-	unsigned long elapsed, tick2, intpending;
+	u32 tmcon;
 
-	/*
-	 * Get the current number of ticks.  Note that there is a race
-	 * condition between us reading the timer and checking for an
-	 * interrupt.  We solve this by ensuring that the counter has not
-	 * reloaded between our two reads.
-	 */
-	elapsed = readl_relaxed(KS8695_TMR_VA + KS8695_T1TC) + readl_relaxed(KS8695_TMR_VA + KS8695_T1PD);
-	do {
-		tick2 = elapsed;
-		intpending = readl_relaxed(KS8695_IRQ_VA + KS8695_INTST) & (1 << KS8695_IRQ_TIMER1);
-		elapsed = readl_relaxed(KS8695_TMR_VA + KS8695_T1TC) + readl_relaxed(KS8695_TMR_VA + KS8695_T1PD);
-	} while (elapsed > tick2);
-
-	/* Convert to number of ticks expired (not remaining) */
-	elapsed = (CLOCK_TICK_RATE / HZ) - elapsed;
-
-	/* Is interrupt pending?  If so, then timer has been reloaded already. */
-	if (intpending)
-		elapsed += (CLOCK_TICK_RATE / HZ);
-
-	/* Convert ticks to usecs */
-	return (unsigned long)(elapsed * (tick_nsec / 1000)) / LATCH;
+	if (mode == CLOCK_EVT_FEAT_PERIODIC) {
+		u32 rate = DIV_ROUND_CLOSEST(KS8695_CLOCK_RATE, HZ);
+		u32 half = DIV_ROUND_CLOSEST(rate, 2);
+
+		/* Disable timer 1 */
+		tmcon = readl_relaxed(KS8695_TMR_VA + KS8695_TMCON);
+		tmcon &= ~TMCON_T1EN;
+		writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
+
+		/* Both registers need to count down */
+		writel_relaxed(half, KS8695_TMR_VA + KS8695_T1TC);
+		writel_relaxed(half, KS8695_TMR_VA + KS8695_T1PD);
+
+		/* Re-enable timer1 */
+		tmcon |= TMCON_T1EN;
+		writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
+	}
+}
+
+static int ks8695_set_next_event(unsigned long cycles,
+				 struct clock_event_device *evt)
+
+{
+	u32 half = DIV_ROUND_CLOSEST(cycles, 2);
+	u32 tmcon;
+
+	/* Disable timer 1 */
+	tmcon = readl_relaxed(KS8695_TMR_VA + KS8695_TMCON);
+	tmcon &= ~TMCON_T1EN;
+	writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
+
+	/* Both registers need to count down */
+	writel_relaxed(half, KS8695_TMR_VA + KS8695_T1TC);
+	writel_relaxed(half, KS8695_TMR_VA + KS8695_T1PD);
+
+	/* Re-enable timer1 */
+	tmcon |= TMCON_T1EN;
+	writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
+
+	return 0;
 }
 
+static struct clock_event_device clockevent_ks8695 = {
+	.name		= "ks8695_t1tc",
+	.rating		= 300, /* Reasonably fast and accurate clock event */
+	.features	= CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC,
+	.set_next_event	= ks8695_set_next_event,
+	.set_mode	= ks8695_set_mode,
+};
+
 /*
  * IRQ handler for the timer.
  */
 static irqreturn_t ks8695_timer_interrupt(int irq, void *dev_id)
 {
-	timer_tick();
+	struct clock_event_device *evt = &clockevent_ks8695;
+
+	evt->event_handler(evt);
 	return IRQ_HANDLED;
 }
 
@@ -102,18 +128,22 @@ static struct irqaction ks8695_timer_irq = {
 
 static void ks8695_timer_setup(void)
 {
-	unsigned long tmout = CLOCK_TICK_RATE / HZ;
 	unsigned long tmcon;
 
-	/* disable timer1 */
+	/* Disable timer 0 and 1 */
 	tmcon = readl_relaxed(KS8695_TMR_VA + KS8695_TMCON);
-	writel_relaxed(tmcon & ~TMCON_T1EN, KS8695_TMR_VA + KS8695_TMCON);
-
-	writel_relaxed(tmout / 2, KS8695_TMR_VA + KS8695_T1TC);
-	writel_relaxed(tmout / 2, KS8695_TMR_VA + KS8695_T1PD);
+	tmcon &= ~TMCON_T0EN;
+	tmcon &= ~TMCON_T1EN;
+	writel_relaxed(tmcon, KS8695_TMR_VA + KS8695_TMCON);
 
-	/* re-enable timer1 */
-	writel_relaxed(tmcon | TMCON_T1EN, KS8695_TMR_VA + KS8695_TMCON);
+	/*
+	 * Use timer 1 to fire IRQs on the timeline, minimum 2 cycles
+	 * (one on each counter) maximum 2*2^32, but the API will only
+	 * accept up to a 32bit full word (0xFFFFFFFFU).
+	 */
+	clockevents_config_and_register(&clockevent_ks8695,
+					KS8695_CLOCK_RATE, 2,
+					0xFFFFFFFFU);
 }
 
 static void __init ks8695_timer_init (void)
@@ -126,7 +156,6 @@ static void __init ks8695_timer_init (void)
 
 struct sys_timer ks8695_timer = {
 	.init		= ks8695_timer_init,
-	.offset		= ks8695_gettimeoffset,
 };
 
 void ks8695_restart(char mode, const char *cmd)