From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753967Ab1JKAqr (ORCPT ); Mon, 10 Oct 2011 20:46:47 -0400 Received: from dns1.mips.com ([12.201.5.69]:60804 "EHLO dns1.mips.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753083Ab1JKAqq convert rfc822-to-8bit (ORCPT ); Mon, 10 Oct 2011 20:46:46 -0400 X-Greylist: delayed 3242 seconds by postgrey-1.27 at vger.kernel.org; Mon, 10 Oct 2011 20:46:45 EDT From: "Zhu, DengCheng" To: Bjorn Helgaas CC: "jbarnes@virtuousgeek.org" , "ralf@linux-mips.org" , "monstr@monstr.eu" , "benh@kernel.crashing.org" , "paulus@samba.org" , "davem@davemloft.net" , "tglx@linutronix.de" , "mingo@redhat.com" , "hpa@zytor.com" , "x86@kernel.org" , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mips@linux-mips.org" , "Barzilay, Eyal" , "Fortuna, Zenon" , "dengcheng.zhu@gmail.com" Subject: RE: [RESEND PATCH v3 0/2] Pass resources to pci_create_bus() and fix MIPS PCI resources Thread-Topic: [RESEND PATCH v3 0/2] Pass resources to pci_create_bus() and fix MIPS PCI resources Thread-Index: AQHMaFGlI7Hp27+M00OrntK+WpTVnJVyGw+AgASqA4D//68aHQ== Date: Mon, 10 Oct 2011 23:49:06 +0000 Message-ID: References: <1314845309-3277-1-git-send-email-dczhu@mips.com> , In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [192.168.36.79] x-ems-proccessed: 6LP3oGfGVdcdb8o1aBnt6w== x-ems-stamp: iiay/VHfaASoyHWbbhfuEw== Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2011/10/11 Bjorn Helgaas > > On Fri, Oct 7, 2011 at 3:50 PM, Bjorn Helgaas wrote: > > On Wed, Aug 31, 2011 at 8:48 PM, Deng-Cheng Zhu wrote: > >> (Resending the patch set to include more arch maintainers.) > >> > >> Change the pci_create_bus() interface to pass in available resources to get them > >> settled down early. This is to avoid possible resource conflicts while doing > >> pci_scan_slot() in pci_scan_child_bus(). Note that pcibios_fixup_bus() can get > >> rid of such conflicts, but it's done AFTER scanning slots. > >> > >> In addition, MIPS PCI resources are now fixed using this new interface. > > > > Jesse, I assume these are headed for the 3.2 merge window, right? > > I tried to build on these patches to convert x86 to using the new > pci_create_bus() interface, but I couldn't figure out a nice way to > handle an arbitrary number of resources. > > We made pci_create_bus() take a "struct pci_bus_resource *" > (https://lkml.org/lkml/2011/8/26/88): > > struct pci_bus *pci_create_bus(struct device *parent, int bus, > struct pci_ops *ops, void *sysdata, > struct pci_bus_resource *bus_res); > > Where pci_bus_resource looks like this: > > struct pci_bus_resource { > struct list_head list; > struct resource *res; > unsigned int flags; > }; > > Conceptually, we're passing a list of resources to pci_create_bus(), > which I think is the right thing. But I think the best way to do that > is by passing a pointer to a struct list_head, not a pointer to a > pci_bus_resource. > > If we pass a pci_bus_resource, we're basically using that as a > container for a list (as per include/linux/list.h), but it's not a > well-formed list. Normally a list contains one list_head per element, > plus an extra list_head for the head of the list. There's a nice > drawing on page 296 of http://lwn.net/images/pdf/LDD3/ch11.pdf. > > The list built in your MIPS patch (https://lkml.org/lkml/2011/8/26/89) > consists of two pci_bus_resource structs (each with a list_head), but > there's no third list_head for the head of the list. I think if you > tried to use list_for_each_entry() to iterate through the list, it > would not work correctly. > > I'll post a slightly modified series to show what I mean. Take a look > and see if it makes sense to you. Yes, I can easily understand what you mean, because this point was ever considered while writing this patch series. We pass the element list as opposed to a list_head for the head of the element list because we simply want to link the elements into pci_bus->resources in pci_create_bus(). This can be done by a single line: list_add_tail(&b->resources, &bus_res->list); In addition, if we need to do list_for_each_entry() on the list, our target should always be pci_bus->resources rather than the pci_bus_resource list which is passed into pci_create_bus() to be part (the meat) of pci_bus->resources. Deng-Cheng