From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932464Ab0BDTUZ (ORCPT ); Thu, 4 Feb 2010 14:20:25 -0500 Received: from one.firstfloor.org ([213.235.205.2]:59134 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932227Ab0BDTUW (ORCPT ); Thu, 4 Feb 2010 14:20:22 -0500 Date: Thu, 4 Feb 2010 20:20:20 +0100 From: Andi Kleen To: tglx@linutronix.de, linux-kernel@vger.kernel.org, venkatesh.pallipadi@intel.com Subject: [PATCH] HPET: Drop WARN_ON for mismatch on HPET CMP readback II Message-ID: <20100204192020.GA10323@basil.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [AK: Sorry, here's the version that actually compiles. Forgot to do the final commit to git] HPET: Drop WARN_ON for mismatch on HPET CMP readback At least one Intel chipset seems to always return a constant value when reading back the HPET CMP register. This triggers the WARN_ON_ONCE on each boot. In addition the WARN_ON was buggy: it has a side-effect and actually needed code could be optimized out if someone disabled CONFIG_BUG. So far there's no indication that miscompare on reading points to actual problem. So simply drop the WARN_ON_ONCE. Based on discussions with Thomas Gleixner. Signed-off-by: Andi Kleen diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index ad80a1c..c7eb16f 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -394,14 +394,11 @@ static int hpet_next_event(unsigned long delta, * at that point and we would wait for the next hpet interrupt * forever. We found out that reading the CMP register back * forces the transfer so we can rely on the comparison with - * the counter register below. If the read back from the - * compare register does not match the value we programmed - * then we might have a real hardware problem. We can not do - * much about it here, but at least alert the user/admin with - * a prominent warning. + * the counter register below. + * But don't actually check the read-back value. Some Intel chipsets + * return always the same value. */ - WARN_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt, - KERN_WARNING "hpet: compare register read back failed.\n"); + (void)hpet_readl(HPET_Tn_CMP(timer)); return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0; }