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MIPS: Kernel hangs occasionally during boot.

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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>
This commit is contained in:
Al Cooper 2011-11-08 09:59:01 -05:00 committed by Ralf Baechle
parent e63fb7a9da
commit 4f1a1eb530
1 changed files with 19 additions and 19 deletions
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38
arch/mips/kernel/cevt-r4k.c
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@ -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;