From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754880Ab0CQN0w (ORCPT ); Wed, 17 Mar 2010 09:26:52 -0400 Received: from mga12.intel.com ([143.182.124.36]:4279 "EHLO azsmga102.ch.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751011Ab0CQN0t (ORCPT ); Wed, 17 Mar 2010 09:26:49 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.49,657,1262592000"; d="scan'208";a="255664108" Date: Wed, 17 Mar 2010 13:01:59 +0000 From: Alan Cox To: Simon Kagstrom Cc: x86@kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org, hpa@zytor.com Subject: Re: [PATCH 1/2]: serial8250: Use native_io_delay on the x86 Message-ID: <20100317130159.23d1103f@linux.intel.com> In-Reply-To: <20100317133050.54851ff8@marrow.netinsight.se> References: <20100317132849.7d49939b@marrow.netinsight.se> <20100317133050.54851ff8@marrow.netinsight.se> Organization: Intel X-Mailer: Claws Mail 3.7.4 (GTK+ 2.18.6; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 17 Mar 2010 13:30:50 +0100 Simon Kagstrom wrote: > Port 0x80 is not safe to use on all x86 boards (see > arch/x86/kernel/io_delay.c), so use native_io_delay instead. > > Signed-off-by: Simon Kagstrom native_io_delay() won't work if the system is being run with no delays. The I/O cycle isn't for the delay but to force the bus signals. So in various modes (paravirt, udelay, no delay) the native_io_delay won't actually do what is required. I'm actually surprised you hit this path and if anything the right fix is to avoid hitting this kind of probing in the first place.