From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: [PATCH 1/2]: serial8250: Use native_io_delay on the x86 Date: Wed, 17 Mar 2010 13:01:59 +0000 Message-ID: <20100317130159.23d1103f@linux.intel.com> References: <20100317132849.7d49939b@marrow.netinsight.se> <20100317133050.54851ff8@marrow.netinsight.se> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: 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 In-Reply-To: <20100317133050.54851ff8@marrow.netinsight.se> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org 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 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.