CRIS: GENERIC_TIME fixes

GENERIC_TIME was not functional for CRIS, giving random backward
time jumps.

For CRISv32 implement a new clocksource using the free running counter
and ditch the arch_gettimeoffset.

The random time jumps still existed, but turned out to be the write_seqlock
which was missing around our do_timer() call.

So switch over to GENERIC_TIME using the clocksource for CRISv32.

CRISv10 doesn't have the free running counter needed for the
clocksource trick, but we can still use GENERIC_TIME with
arch_gettimeoffset.

Unfortunately, there were problems in using the prescaler register
to timer0 for the gettimeoffset calculation, so it is now ignored,
making our resolution worse by the tune of 40usec (0.4%) worst case.

At the same time, clean up some formatting and use NSEC_PER_SEC
instead of 1000000000.

Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>

1 files changed, 2 insertions, 52 deletions

diff --git a/arch/cris/arch-v10/kernel/time.c b/arch/cris/arch-v10/kernel/time.c
index 30adae594aef..00eb36f8debf 100644
--- a/arch/cris/arch-v10/kernel/time.c
+++ b/arch/cris/arch-v10/kernel/time.c
@@ -61,66 +61,16 @@ unsigned long get_ns_in_jiffie(void)
 
 unsigned long do_slow_gettimeoffset(void)
 {
-        unsigned long count, t1;
-        unsigned long usec_count = 0;
-        unsigned short presc_count;
-
-        static unsigned long count_p = TIMER0_DIV;/* for the first call after boot */
-        static unsigned long jiffies_p = 0;
-
-        /*
-         * cache volatile jiffies temporarily; we have IRQs turned off. 
-         */
-        unsigned long jiffies_t;
+        unsigned long count;
 
         /* The timer interrupt comes from Etrax timer 0. In order to get
          * better precision, we check the current value. It might have
          * underflowed already though.
          */
-
-#ifndef CONFIG_SVINTO_SIM
-        /* Not available in the xsim simulator. */
         count = *R_TIMER0_DATA;
-        presc_count = *R_TIM_PRESC_STATUS;  
-        /* presc_count might be wrapped */
-        t1 = *R_TIMER0_DATA;
-        if (count != t1){
-                /* it wrapped, read prescaler again...  */
-                presc_count = *R_TIM_PRESC_STATUS;
-                count = t1;
-        }
-#else
-        count = 0;
-        presc_count = 0;
-#endif
-
-        jiffies_t = jiffies;
 
-        /*
-         * avoiding timer inconsistencies (they are rare, but they happen)...
-         * there are one problem that must be avoided here:
-         *  1. the timer counter underflows
-         */
-        if( jiffies_t == jiffies_p ) {
-                if( count > count_p ) {
-                        /* Timer wrapped, use new count and prescale 
-                         * increase the time corresponding to one jiffie
-                         */
-                        usec_count = 1000000/HZ;
-                }
-        } else
-                jiffies_p = jiffies_t;
-        count_p = count;
-        if (presc_count >= PRESCALE_VALUE/2 ){
-                presc_count =  PRESCALE_VALUE - presc_count + PRESCALE_VALUE/2;
-        } else {
-                presc_count =  PRESCALE_VALUE - presc_count - PRESCALE_VALUE/2;
-        }
         /* Convert timer value to usec */
-        usec_count += ( (TIMER0_DIV - count) * (1000000/HZ)/TIMER0_DIV ) +
-                      (( (presc_count) * (1000000000/PRESCALE_FREQ))/1000);
-
-        return usec_count;
+        return (TIMER0_DIV - count) * ((NSEC_PER_SEC/1000)/HZ)/TIMER0_DIV;
 }
 
 /* Excerpt from the Etrax100 HSDD about the built-in watchdog: