The Kernel hangs occasionally during boot after
"Calibrating delay loop..". This is caused by the
c0_compare_int_usable() routine in cevt-r4k.c returning false which
causes the system to disable the timer and hang later. The false
return happens because the routine is using a series of four calls to
irq_disable_hazard() as a delay while it waits for the timer changes
to propagate to the cp0 cause register. On newer MIPS cores, like the 74K,
the series of irq_disable_hazard() calls turn into ehb instructions and
can take as little as a few clock ticks for all 4 instructions. This
is not enough of a delay, so the routine thinks the timer is not working.
This fix uses up to a max number of cycle counter ticks for the delay
and uses back_to_back_c0_hazard() instead of irq_disable_hazard() to
handle the hazard condition between cp0 writes and cp0 reads.
Signed-off-by: Al Cooper <alcooperx@xxxxxxxxx>
---
arch/mips/kernel/cevt-r4k.c | 38 +++++++++++++++++++-------------------
1 files changed, 19 insertions(+), 19 deletions(-)
diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
index 98c5a97..e2d8e19 100644
--- a/arch/mips/kernel/cevt-r4k.c
+++ b/arch/mips/kernel/cevt-r4k.c
@@ -103,19 +103,10 @@ static int c0_compare_int_pending(void)
/*
* Compare interrupt can be routed and latched outside the core,
- * so a single execution hazard barrier may not be enough to give
- * it time to clear as seen in the Cause register. 4 time the
- * pipeline depth seems reasonably conservative, and empirically
- * works better in configurations with high CPU/bus clock ratios.
+ * so wait up to worst case number of cycle counter ticks for timer interrupt
+ * changes to propagate to the cause register.
*/
-
-#define compare_change_hazard() \
- do { \
- irq_disable_hazard(); \
- irq_disable_hazard(); \
- irq_disable_hazard(); \
- irq_disable_hazard(); \
- } while (0)
+#define COMPARE_INT_SEEN_TICKS 50
int c0_compare_int_usable(void)
{
@@ -126,8 +117,12 @@ int c0_compare_int_usable(void)
* IP7 already pending? Try to clear it by acking the timer.
*/
if (c0_compare_int_pending()) {
- write_c0_compare(read_c0_count());
- compare_change_hazard();
+ cnt = read_c0_count();
+ write_c0_compare(cnt);
+ back_to_back_c0_hazard();
+ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
+ if (!c0_compare_int_pending())
+ break;
if (c0_compare_int_pending())
return 0;
}
@@ -136,7 +131,7 @@ int c0_compare_int_usable(void)
cnt = read_c0_count();
cnt += delta;
write_c0_compare(cnt);
- compare_change_hazard();
+ back_to_back_c0_hazard();
if ((int)(read_c0_count() - cnt) < 0)
break;
/* increase delta if the timer was already expired */
@@ -145,12 +140,17 @@ int c0_compare_int_usable(void)
while ((int)(read_c0_count() - cnt) <= 0)
; /* Wait for expiry */
- compare_change_hazard();
+ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
+ if (c0_compare_int_pending())
+ break;
if (!c0_compare_int_pending())
return 0;
-
- write_c0_compare(read_c0_count());
- compare_change_hazard();
+ cnt = read_c0_count();
+ write_c0_compare(cnt);
+ back_to_back_c0_hazard();
+ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
+ if (!c0_compare_int_pending())
+ break;
if (c0_compare_int_pending())
return 0;
--
1.7.6
