From 47d2e117d6463a5a9ac36f1391ce31a9a34929c8 Mon Sep 17 00:00:00 2001 From: Russell King Date: Wed, 5 Oct 2016 23:40:43 +0100 Subject: [PATCH] ARM: fix delays commit fb833b1fbb68461772dbf5e91bddea5e839187e9 upstream. 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") Reviewed-by: Nicolas Pitre Signed-off-by: Russell King Signed-off-by: Greg Kroah-Hartman --- arch/arm/include/asm/delay.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) 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 /* 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__ -- 2.34.1