Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755268AbcJNM3o (ORCPT ); Fri, 14 Oct 2016 08:29:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:41014 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755549AbcJNM2a (ORCPT ); Fri, 14 Oct 2016 08:28:30 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicolas Pitre , Russell King Subject: [PATCH 4.8 29/37] ARM: fix delays Date: Fri, 14 Oct 2016 14:27:15 +0200 Message-Id: <20161014122553.988073773@linuxfoundation.org> X-Mailer: git-send-email 2.10.0 In-Reply-To: <20161014122549.411962735@linuxfoundation.org> References: <20161014122549.411962735@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1765 Lines: 57 4.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Russell King 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(-) --- 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__