clocksource/drivers/lpc32xx: Don't use the prescaler counter for clockevents

This commit switches the clockevents one-shot current implementation
to avoid using the prescaler counter. The clockevents timer currently
uses MR0=1, PR=ticks; and after this commit is uses MR0=ticks, PR=0.

While using the prescaler with PR=1 works fine in one-shot mode,
it seems it doesn't work as expected in periodic mode.

By using the only match channel register (MR0) for the timer we make
the periodic mode introduction easier, and consistent with one-shot mode.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Joachim Eastwood <manabian@gmail.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>

drivers/clocksource/time-lpc32xx.c

@@ -60,14 +60,13 @@ static int lpc32xx_clkevt_next_event(unsigned long delta,
 		container_of(evtdev, struct lpc32xx_clock_event_ddata, evtdev);
 
 	/*
-	 * Place timer in reset and program the delta in the prescale
-	 * register (PR). When the prescale counter matches the value
-	 * in PR the counter register is incremented and the compare
-	 * match will trigger. After setup the timer is released from
-	 * reset and enabled.
+	 * Place timer in reset and program the delta in the match
+	 * channel 0 (MR0). When the timer counter matches the value
+	 * in MR0 register the match will trigger an interrupt.
+	 * After setup the timer is released from reset and enabled.
 	 */
 	writel_relaxed(LPC32XX_TIMER_TCR_CRST, ddata->base + LPC32XX_TIMER_TCR);
-	writel_relaxed(delta, ddata->base + LPC32XX_TIMER_PR);
+	writel_relaxed(delta, ddata->base + LPC32XX_TIMER_MR0);
 	writel_relaxed(LPC32XX_TIMER_TCR_CEN, ddata->base + LPC32XX_TIMER_TCR);
 
 	return 0;
@@ -210,13 +209,13 @@ static int __init lpc32xx_clockevent_init(struct device_node *np)
 
 	/*
 	 * Disable timer and clear any pending interrupt (IR) on match
-	 * channel 0 (MR0). Configure a compare match value of 1 on MR0
-	 * and enable interrupt, reset on match and stop on match (MCR).
+	 * channel 0 (MR0). Clear the prescaler as it's not used.
+	 * Enable interrupt, reset on match and stop on match (MCR).
 	 */
 	writel_relaxed(0, base + LPC32XX_TIMER_TCR);
+	writel_relaxed(0, base + LPC32XX_TIMER_PR);
 	writel_relaxed(0, base + LPC32XX_TIMER_CTCR);
 	writel_relaxed(LPC32XX_TIMER_IR_MR0INT, base + LPC32XX_TIMER_IR);
-	writel_relaxed(1, base + LPC32XX_TIMER_MR0);
 	writel_relaxed(LPC32XX_TIMER_MCR_MR0I | LPC32XX_TIMER_MCR_MR0R |
 		       LPC32XX_TIMER_MCR_MR0S, base + LPC32XX_TIMER_MCR);