[PATCH] arc: make sure __delay() never gets executed with 0 loops
From: Alexey Brodkin
Date: Mon Feb 15 2016 - 11:38:03 EST
Current implementation of __delay() function uses so-called
zero-delay loops. And the only condition to exit that loop is
LP_COUNT (loop count register) = 1 (but not 0 as it might be easily
imagined).
So if our calculation of "loops" gives 0 (and that is pretty possible
given result of multiplication being >> 32) then zero-delay loop
mechanism starts with LP_COUNT=0 and it ends up decrementing LP_COUNT
while staying in the loop effectively producing close to infinite delay
instead of very short one.
I bumped into it with AXS101 + external DDR controller and caches
disabled. In that case I've got very small
loops_per_jiffy=0xf00:
------------------------>8--------------------
Calibrating delay loop... 0.77 BogoMIPS (lpj=3862)
------------------------>8--------------------
And on console output delays were way too long.
Signed-off-by: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Please enter the commit message for your changes. Lines starting
---
arch/arc/include/asm/delay.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arc/include/asm/delay.h b/arch/arc/include/asm/delay.h
index 08e7e2a..1a7a1dc 100644
--- a/arch/arc/include/asm/delay.h
+++ b/arch/arc/include/asm/delay.h
@@ -57,7 +57,8 @@ static inline void __udelay(unsigned long usecs)
*/
loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
- __delay(loops);
+ if (loops)
+ __delay(loops);
}
#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
--
2.4.3