m68knommu: init coldfire timer TRR with n - 1, not n

The coldfire timer must be initialised to n - 1 if we want it to count n
cycles between each tick interrupt.  This was already fixed, but has been
lost with the conversion to GENERIC_TIMER.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Acked-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/m68knommu/platform/coldfire/timers.c b/arch/m68knommu/platform/coldfire/timers.c
index ba5a9f32ebd4..454f25493491 100644
--- a/arch/m68knommu/platform/coldfire/timers.c
+++ b/arch/m68knommu/platform/coldfire/timers.c
@@ -111,7 +111,13 @@ void hw_timer_init(void)
 
         __raw_writew(MCFTIMER_TMR_DISABLE, TA(MCFTIMER_TMR));
         mcftmr_cycles_per_jiffy = FREQ / HZ;
-        __raw_writetrr(mcftmr_cycles_per_jiffy, TA(MCFTIMER_TRR));
+        /*
+         *      The coldfire timer runs from 0 to TRR included, then 0
+         *      again and so on.  It counts thus actually TRR + 1 steps
+         *      for 1 tick, not TRR.  So if you want n cycles,
+         *      initialize TRR with n - 1.
+         */
+        __raw_writetrr(mcftmr_cycles_per_jiffy - 1, TA(MCFTIMER_TRR));
         __raw_writew(MCFTIMER_TMR_ENORI | MCFTIMER_TMR_CLK16 |
                 MCFTIMER_TMR_RESTART | MCFTIMER_TMR_ENABLE, TA(MCFTIMER_TMR));