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authorRussell King <rmk+kernel@armlinux.org.uk>2016-10-05 23:40:43 +0100
committerRussell King <rmk+kernel@armlinux.org.uk>2016-10-06 08:45:40 +0100
commitfb833b1fbb68461772dbf5e91bddea5e839187e9 (patch)
treea3866847afd0c0b8ac2a9d61addb8fc9861b7586
parent117e5e9c4cfcb7628f08de074fbfefec1bb678b7 (diff)
ARM: fix delays
Commit 215e362dafed ("ARM: 8306/1: loop_udelay: remove bogomips value limitation") tried to increase the bogomips limitation, but in doing so messed up udelay such that it always gives about a 5% error in the delay, even if we use a timer. The calculation is: loops = UDELAY_MULT * us_delay * ticks_per_jiffy >> UDELAY_SHIFT Originally, UDELAY_MULT was ((UL(2199023) * HZ) >> 11) and UDELAY_SHIFT 30. Assuming HZ=100, us_delay of 1000 and ticks_per_jiffy of 1660000 (eg, 166MHz timer, 1ms delay) this would calculate: ((UL(2199023) * HZ) >> 11) * 1000 * 1660000 >> 30 => 165999 With the new values of 2047 * HZ + 483648 * HZ / 1000000 and 31, we get: (2047 * HZ + 483648 * HZ / 1000000) * 1000 * 1660000 >> 31 => 158269 which is incorrect. This is due to a typo - correcting it gives: (2147 * HZ + 483648 * HZ / 1000000) * 1000 * 1660000 >> 31 => 165999 i.o.w, the original value. Fixes: 215e362dafed ("ARM: 8306/1: loop_udelay: remove bogomips value limitation") Cc: <stable@vger.kernel.org> Reviewed-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
-rw-r--r--arch/arm/include/asm/delay.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index b7a428154355..b1ce037e4380 100644
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -10,7 +10,7 @@
#include <asm/param.h> /* HZ */
#define MAX_UDELAY_MS 2
-#define UDELAY_MULT UL(2047 * HZ + 483648 * HZ / 1000000)
+#define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000)
#define UDELAY_SHIFT 31
#ifndef __ASSEMBLY__