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authorAl Cooper <alcooperx@gmail.com>2011-11-08 09:59:01 -0500
committerRalf Baechle <ralf@linux-mips.org>2011-11-08 17:59:22 +0000
commit4f1a1eb530071c39fb239fd26c912a64284b1408 (patch)
treee4b00b9dab468604f97e2fbe1585ba0e87f37991 /arch/mips/kernel/cevt-r4k.c
parente63fb7a9dae820b3ff6754f794fd713f83e32fff (diff)
MIPS: Kernel hangs occasionally during boot.
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@gmail.com> Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/2911/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Diffstat (limited to 'arch/mips/kernel/cevt-r4k.c')
-rw-r--r--arch/mips/kernel/cevt-r4k.c38
1 files changed, 19 insertions, 19 deletions
diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
index 98c5a9737c14..e2d8e199be32 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;