m68k: bvme6000: Convert to clocksource API

Add a platform clocksource by adapting the existing arch_gettimeoffset
implementation.
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/bvme6000/config.c

@@ -18,6 +18,7 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/tty.h>
+#include <linux/clocksource.h>
 #include <linux/console.h>
 #include <linux/linkage.h>
 #include <linux/init.h>
@@ -147,6 +148,21 @@ irqreturn_t bvme6000_abort_int (int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static u64 bvme6000_read_clk(struct clocksource *cs);
+
+static struct clocksource bvme6000_clk = {
+	.name   = "rtc",
+	.rating = 250,
+	.read   = bvme6000_read_clk,
+	.mask   = CLOCKSOURCE_MASK(32),
+	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static u32 clk_total, clk_offset;
+
+#define RTC_TIMER_CLOCK_FREQ 8000000
+#define RTC_TIMER_CYCLES     (RTC_TIMER_CLOCK_FREQ / HZ)
+#define RTC_TIMER_COUNT      ((RTC_TIMER_CYCLES / 2) - 1)
 
 static irqreturn_t bvme6000_timer_int (int irq, void *dev_id)
 {
@@ -158,6 +174,8 @@ static irqreturn_t bvme6000_timer_int (int irq, void *dev_id)
     local_irq_save(flags);
     msr = rtc->msr & 0xc0;
     rtc->msr = msr | 0x20;		/* Ack the interrupt */
+    clk_total += RTC_TIMER_CYCLES;
+    clk_offset = 0;
     timer_routine(0, NULL);
     local_irq_restore(flags);
 
@@ -180,13 +198,13 @@ void bvme6000_sched_init (irq_handler_t timer_routine)
 
     rtc->msr = 0;	/* Ensure timer registers accessible */
 
-    if (request_irq(BVME_IRQ_RTC, bvme6000_timer_int, 0, "timer",
+    if (request_irq(BVME_IRQ_RTC, bvme6000_timer_int, IRQF_TIMER, "timer",
                     timer_routine))
 	panic ("Couldn't register timer int");
 
     rtc->t1cr_omr = 0x04;	/* Mode 2, ext clk */
-    rtc->t1msb = 39999 >> 8;
-    rtc->t1lsb = 39999 & 0xff;
+    rtc->t1msb = RTC_TIMER_COUNT >> 8;
+    rtc->t1lsb = RTC_TIMER_COUNT & 0xff;
     rtc->irr_icr1 &= 0xef;	/* Route timer 1 to INTR pin */
     rtc->msr = 0x40;		/* Access int.cntrl, etc */
     rtc->pfr_icr0 = 0x80;	/* Just timer 1 ints enabled */
@@ -198,14 +216,14 @@ void bvme6000_sched_init (irq_handler_t timer_routine)
 
     rtc->msr = msr;
 
+    clocksource_register_hz(&bvme6000_clk, RTC_TIMER_CLOCK_FREQ);
+
     if (request_irq(BVME_IRQ_ABORT, bvme6000_abort_int, 0,
 				"abort", bvme6000_abort_int))
 	panic ("Couldn't register abort int");
 }
 
 
-/* This is always executed with interrupts disabled.  */
-
 /*
  * NOTE:  Don't accept any readings within 5us of rollover, as
  * the T1INT bit may be a little slow getting set.  There is also
@@ -213,14 +231,18 @@ void bvme6000_sched_init (irq_handler_t timer_routine)
  * results...
  */
 
-u32 bvme6000_gettimeoffset(void)
+static u64 bvme6000_read_clk(struct clocksource *cs)
 {
+    unsigned long flags;
     volatile RtcPtr_t rtc = (RtcPtr_t)BVME_RTC_BASE;
     volatile PitRegsPtr pit = (PitRegsPtr)BVME_PIT_BASE;
-    unsigned char msr = rtc->msr & 0xc0;
+    unsigned char msr, msb;
     unsigned char t1int, t1op;
     u32 v = 800000, ov;
 
+    local_irq_save(flags);
+
+    msr = rtc->msr & 0xc0;
     rtc->msr = 0;	/* Ensure timer registers accessible */
 
     do {
@@ -228,22 +250,25 @@ u32 bvme6000_gettimeoffset(void)
 	t1int = rtc->msr & 0x20;
 	t1op  = pit->pcdr & 0x04;
 	rtc->t1cr_omr |= 0x40;		/* Latch timer1 */
-	v = rtc->t1msb << 8;		/* Read timer1 */
-	v |= rtc->t1lsb;		/* Read timer1 */
+	msb = rtc->t1msb;		/* Read timer1 */
+	v = (msb << 8) | rtc->t1lsb;	/* Read timer1 */
     } while (t1int != (rtc->msr & 0x20) ||
 		t1op != (pit->pcdr & 0x04) ||
 			abs(ov-v) > 80 ||
-				v > 39960);
+				v > RTC_TIMER_COUNT - (RTC_TIMER_COUNT / 100));
 
-    v = 39999 - v;
+    v = RTC_TIMER_COUNT - v;
     if (!t1op)				/* If in second half cycle.. */
-	v += 40000;
-    v /= 8;				/* Convert ticks to microseconds */
-    if (t1int)
-	v += 10000;			/* Int pending, + 10ms */
+	v += RTC_TIMER_CYCLES / 2;
+    if (msb > 0 && t1int)
+	clk_offset = RTC_TIMER_CYCLES;
     rtc->msr = msr;
 
-    return v * 1000;
+    v += clk_offset + clk_total;
+
+    local_irq_restore(flags);
+
+    return v;
 }
 
 /*