From: <gregkh@linuxfoundation.org>
To: rmk+kernel@armlinux.org.uk, gregkh@linuxfoundation.org, nico@linaro.org
Cc: <stable@vger.kernel.org>, <stable-commits@vger.kernel.org>
Subject: Patch "ARM: fix delays" has been added to the 4.8-stable tree
Date: Fri, 14 Oct 2016 12:00:40 +0200 [thread overview]
Message-ID: <147643924023886@kroah.com> (raw)
This is a note to let you know that I've just added the patch titled
ARM: fix delays
to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm-fix-delays.patch
and it can be found in the queue-4.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.
>From fb833b1fbb68461772dbf5e91bddea5e839187e9 Mon Sep 17 00:00:00 2001
From: Russell King <rmk+kernel@armlinux.org.uk>
Date: Wed, 5 Oct 2016 23:40:43 +0100
Subject: ARM: fix delays
From: Russell King <rmk+kernel@armlinux.org.uk>
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 <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/include/asm/delay.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 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__
Patches currently in stable-queue which might be from rmk+kernel@armlinux.org.uk are
queue-4.8/arm-fix-delays.patch
reply other threads:[~2016-10-14 10:00 UTC|newest]
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