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authorVineet Gupta <vgupta@synopsys.com>2013-02-06 15:09:13 +0530
committerVineet Gupta <vgupta@synopsys.com>2013-02-15 23:16:20 +0530
commit1e266629933bb3e40ac7db128f3b661f5bab56c1 (patch)
tree9167653a32f9402e5941e5afc24e3eb3019425c5 /arch/arc/kernel
parentd626f547dd0457ab36f6151673fcc78fc3c63eaa (diff)
downloadvexpress-lsk-1e266629933bb3e40ac7db128f3b661f5bab56c1.tar.gz
ARC: 64bit RTSC timestamp hardware issue
The 64bit RTSC is not reliable, causing spurious "jumps" in higher word, making Linux timekeeping go bonkers. So as of now just use the lower 32bit timestamp. A cleaner approach would have been removing RTSC support altogether as the 32bit RTSC is equivalent to old TIMER1 based solution, but some customers can use the 32bit RTSC in SMP syn fashion (vs. TIMER1 which being incore can't be done easily). A fallout of this is sched_clock()'s hardware assisted version needs to go away since it can't use 32bit wrapping counter - instead we use the generic "weak" jiffies based version. Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'arch/arc/kernel')
-rw-r--r--arch/arc/kernel/time.c38
1 files changed, 2 insertions, 36 deletions
diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
index 0ce0e6f76eb..f13f72807aa 100644
--- a/arch/arc/kernel/time.c
+++ b/arch/arc/kernel/time.c
@@ -76,7 +76,7 @@ static cycle_t arc_counter_read(struct clocksource *cs)
__asm__ __volatile(
" .extCoreRegister tsch, 58, r, cannot_shortcut \n"
" rtsc %0, 0 \n"
- " mov %1, tsch \n" /* TSCH is extn core reg 58 */
+ " mov %1, 0 \n"
: "=r" (stamp.low), "=r" (stamp.high));
arch_local_irq_restore(flags);
@@ -88,7 +88,7 @@ static struct clocksource arc_counter = {
.name = "ARC RTSC",
.rating = 300,
.read = arc_counter_read,
- .mask = CLOCKSOURCE_MASK(64),
+ .mask = CLOCKSOURCE_MASK(32),
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
@@ -263,37 +263,3 @@ void __init time_init(void)
if (machine_desc->init_time)
machine_desc->init_time();
}
-
-#ifdef CONFIG_ARC_HAS_RTSC
-/*
- * sched_clock math assist
- * ns = cycles * (ns_per_sec / cpu_freq_hz)
- * ns = cycles * (10^6 / cpu_freq_khz)
- * ns = cycles * (10^6 * 2^SF / cpu_freq_khz) / 2^SF
- * ns = cycles * cyc2ns_scale >> SF
- */
-#define CYC2NS_SF 10 /* 2^10, carefully chosen */
-#define CYC2NS_SCALE ((1000000 << CYC2NS_SF) / (arc_get_core_freq() / 1000))
-
-static unsigned long long cycles2ns(unsigned long long cyc)
-{
- return (cyc * CYC2NS_SCALE ) >> CYC2NS_SF;
-}
-
-/*
- * Scheduler clock - a monotonically increasing clock in nanosec units.
- * It's return value must NOT wrap around.
- *
- * - Since 32bit TIMER1 will overflow almost immediately (53sec @ 80MHz), it
- * can't be used directly.
- * - Using getrawmonotonic (TIMER1 based, but with state for last + current
- * snapshots), is no-good either because of seqlock deadlock possibilities
- * - So only with native 64bit timer we do this, otherwise fallback to generic
- * jiffies based version - which despite not being fine grained gaurantees
- * the monotonically increasing semantics.
- */
-unsigned long long sched_clock(void)
-{
- return cycles2ns(arc_counter_read(NULL));
-}
-#endif