From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759469Ab2AMX07 (ORCPT ); Fri, 13 Jan 2012 18:26:59 -0500 Received: from cavan.codon.org.uk ([93.93.128.6]:34045 "EHLO cavan.codon.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753535Ab2AMX05 (ORCPT ); Fri, 13 Jan 2012 18:26:57 -0500 Date: Fri, 13 Jan 2012 23:26:53 +0000 From: Matthew Garrett To: Linus Torvalds Cc: Jesse Barnes , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [git pull] PCI changes Message-ID: <20120113232653.GA29533@srcf.ucam.org> References: <20120111103408.30cfa338@jbarnes-desktop> <20120113212409.GA27671@srcf.ucam.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: mjg59@cavan.codon.org.uk X-SA-Exim-Scanned: No (on cavan.codon.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 13, 2012 at 03:14:21PM -0800, Linus Torvalds wrote: > On Fri, Jan 13, 2012 at 1:24 PM, Matthew Garrett wrote: > >> > >> So why is acpi_pci_root_add() special? Cna you explain that part to me? > > > > pcie_no_aspm() means "Do not permit ASPM to be enabled" - it doesn't > > alter the existing state. pcie_clear_aspm() does that. > > I *know*. > > So look again. > > Why is acpi_pci_root_add() special? > > Because dammit, it does exactly that pcie_clear_aspm() for the > ACPI_FADT_NO_ASPM case. I'm sorry, I thought you were referring to the status quo rather than the patch - I see what you mean now. The intent here is to clear ASPM state if the FADT bit has been set *and* we've got _OSC control, whereas previously we'd clear ASPM state any time the FADT bit was set. There are some machines which (a) set the FADT bit, (b) hand over _OSC control, (c) program the device and (d) crash under certain circumstances if you then try to use it. My assumption here is that the FADT bit *does* mean "clear ASPM state", but only if we've been granted _OSC control. That's the behaviour described in the changelog. -- Matthew Garrett | mjg59@srcf.ucam.org