From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750729AbVH1SJs (ORCPT ); Sun, 28 Aug 2005 14:09:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750736AbVH1SJs (ORCPT ); Sun, 28 Aug 2005 14:09:48 -0400 Received: from isilmar.linta.de ([213.239.214.66]:9136 "EHLO linta.de") by vger.kernel.org with ESMTP id S1750729AbVH1SJr (ORCPT ); Sun, 28 Aug 2005 14:09:47 -0400 Date: Sun, 28 Aug 2005 20:09:41 +0200 From: Dominik Brodowski To: Venkatesh Pallipadi Cc: Andrew Morton , linux-kernel , Len Brown Subject: Re: [PATCH] acpi-cpufreq: Remove P-state read after a P-state write in normal path Message-ID: <20050828180941.GB28994@isilmar.linta.de> Mail-Followup-To: Dominik Brodowski , Venkatesh Pallipadi , Andrew Morton , linux-kernel , Len Brown References: <20050826171052.B27226@unix-os.sc.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050826171052.B27226@unix-os.sc.intel.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Fri, Aug 26, 2005 at 05:10:52PM -0700, Venkatesh Pallipadi wrote: > /* > - * Then we read the 'status_register' and compare the value with the > - * target state's 'status' to make sure the transition was successful. > - * Note that we'll poll for up to 1ms (100 cycles of 10us) before > - * giving up. > + * Assume the write went through when acpi_pstate_strict is not used. > + * As read status_register is an expensive operation and there > + * are no specific error cases where an IO port write will fail. > */ Well, the IO port write itself might not fail, but the transition itself -- and we're reading the _status_ register here, not the control register where we've written to. And 8.4.4.1 of ACPI-sepc 3.0 does specifically mention that transitions _can_ fail, so I think we should handle this possibility. Dominik