From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bh-25.webhostbox.net ([208.91.199.152]:60340 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753963AbbGWQsE (ORCPT ); Thu, 23 Jul 2015 12:48:04 -0400 Message-ID: <55B11AB0.7050002@roeck-us.net> Date: Thu, 23 Jul 2015 09:47:44 -0700 From: Guenter Roeck MIME-Version: 1.0 To: Bjorn Helgaas , Lorenzo Pieralisi CC: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, Ralf Baechle , "James E.J. Bottomley" , Michael Ellerman , Richard Henderson , Benjamin Herrenschmidt , David Howells , Russell King , Tony Luck , "David S. Miller" , Ingo Molnar , Michal Simek , Chris Zankel , Arnd Bergmann , Krzysztof Halasa , Phil Edworthy , Jason Gunthorpe , Jingoo Han , Lucas Stach , Simon Horman , Minghuan Lian , Murali Karicheri , Tanmay Inamdar , Kishon Vijay Abraham I , Thierry Reding , Thomas Petazzoni , Will Deacon , Jayachandran C , Suravee Suthikulpanit Subject: Re: [RFT PATCH v3] PCI: move pci_read_bridge_bases to the generic PCI layer References: <1436439557-21075-1-git-send-email-lorenzo.pieralisi@arm.com> <20150723161257.GZ21967@google.com> In-Reply-To: <20150723161257.GZ21967@google.com> Content-Type: text/plain; charset=windows-1252; format=flowed Sender: linux-pci-owner@vger.kernel.org List-ID: On 07/23/2015 09:12 AM, Bjorn Helgaas wrote: > On Thu, Jul 09, 2015 at 11:59:16AM +0100, Lorenzo Pieralisi wrote: >> When a PCI bus is scanned, upon PCI bridge detection the kernel >> has to read the bridge registers to set-up its resources so that >> the PCI resource hierarchy can be validated properly. >> >> Most if not all architectures read PCI bridge registers in the >> pcibios_fixup_bus hook, that is called by the PCI generic layer >> whenever a PCI bus is scanned. >> >> Since pci_read_bridge_bases is an arch agnostic operation (and it >> is carried out on all architectures) it can be moved to the generic >> PCI layer in order to consolidate code and remove the respective >> calls from the architectures back-ends. >> >> The PCI_PROBE_ONLY flag is not checked before calling >> pci_read_bridge_buses in the generic layer since reading the bridge >> bases is not related to resources assignment; this implies that it >> can be carried out safely on PCI_PROBE_ONLY systems too and should >> not affect architectures (alpha, mips) that check the PCI_PROBE_ONLY >> flag before reading the bridge bases. >> >> Signed-off-by: Lorenzo Pieralisi > > Applied to pci/resource for v4.3, thanks! > > The PCI_PROBE_ONLY text seems backward to me: previously alpha and mips > only called pci_read_bridge_bases() if PCI_PROBE_ONLY was set. After this > patch, alpha and mips systems that do not set PCI_PROBE_ONLY will also call > pci_read_bridge_bases(). > > I really don't know why alpha and mips were like that. It seems backwards. > It seems like we'd want to know the bridge windows if we were assigning > things, but they only read them if they were *not* going to assign things. > > I'm a little uneasy that we might break some alpha or mips system, since > there must have been some reason this was done originally. It'd be ideal > if somebody could test a non-PCI_PROBE_ONLY system. But maybe they're all > obsolete. > For alpha, PCI_PROBE_ONLY is set for two platforms, marvel and titan, out of ~20. mips sets the flag for 6 platforms out of >25. Unlikely that those are the only relevant ones. I could try to run some qemu tests for both architectures, but I have no idea what to look out for. Ideas, anyone ? Guenter