From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f45.google.com (mail-wg0-f45.google.com [74.125.82.45]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id EBCEC1A0A0B for ; Thu, 20 Nov 2014 23:53:55 +1100 (AEDT) Received: by mail-wg0-f45.google.com with SMTP id b13so3662027wgh.18 for ; Thu, 20 Nov 2014 04:53:52 -0800 (PST) Message-ID: <546DE45C.6010306@linaro.org> Date: Thu, 20 Nov 2014 13:53:48 +0100 From: Tomasz Nowicki MIME-Version: 1.0 To: Liviu Dudau Subject: Re: [RFC PATCH 00/16] Refine PCI host bridge scan interfaces References: <1416219710-26088-1-git-send-email-wangyijing@huawei.com> <1463511.o4kE8TX3Bd@wuerfel> <546DD688.60705@linaro.org> <20141120120850.GD9162@bart.dudau.co.uk> In-Reply-To: <20141120120850.GD9162@bart.dudau.co.uk> Content-Type: text/plain; charset=UTF-8; format=flowed Cc: Tony Luck , Russell King , Arnd Bergmann , linux-pci@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Xinwei Hu , Yijing Wang , Thierry Reding , Suravee.Suthikulpanit@amd.com, Bjorn Helgaas , linux-ia64@vger.kernel.org, Thomas Gleixner , Wuyun , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 20.11.2014 13:08, Liviu Dudau wrote: > On Thu, Nov 20, 2014 at 12:54:48PM +0100, Tomasz Nowicki wrote: >> On 17.11.2014 15:13, Arnd Bergmann wrote: >>> On Monday 17 November 2014 18:21:34 Yijing Wang wrote: >>>> This series is based Linux 3.18-rc1 and Lorenzo Pieralisi's >>>> arm PCI domain cleanup patches, link: >>>> https://patchwork.ozlabs.org/patch/407585/ >>>> >>>> Current pci scan interfaces like pci_scan_root_bus() and directly >>>> call pci_create_root_bus()/pci_scan_child_bus() lack flexiblity. >>>> Some platform infos like PCI domain and msi_chip have to be >>>> associated to PCI bus by some arch specific function. >>>> We want to make a generic pci_host_bridge, and make it hold >>>> the platform infos or hook. Then we could eliminate the lots >>>> of arch pci_domain_nr, also we could associate some platform >>>> ops something like pci_get_msi_chip(struct pci_dev *dev) >>>> with pci_host_bridge to avoid introduce arch weak functions. >>>> >>>> This RFC version not for all platforms, just applied the new >>>> scan interface in x86/arm/powerpc/ia64, I will refresh other >>>> platforms after the core pci scan interfaces are ok. >>> >>> I think overall this is a good direction to take, in particular >>> moving more things into struct pci_host_bridge so we can >>> slim down the architecture specific code. >>> >>> I don't particularly like the way you use the 'pci_host_info' >>> to pass callback pointers and some of the generic information. >>> This duplicates some of the issues we are currently trying >>> to untangle in the arm32 code to make drivers easier to share >>> between architectures. >>> >>> As a general approach, I'd rather see generic helper functions >>> being exported by the PCI core that a driver may or may not >>> call. >>> The way you split the interface between things that happen >>> before scanning the buses (pci_create_host_bridge) and >>> the actual scanning (__pci_create_root_bus, pci_scan_child_bus) >>> seems very helpful and I think we can expand that concept further: >>> >>> - The normal pci_create_host_bridge() function can contain >>> all of the DT scanning functions (finding bus/mem/io resources, >>> finding the msi-parent), while drivers that don't depend on DT >>> for this information can call the same function and fill the >>> same things after they have the pci_host_bridge pointer. >> >> How about finding PCI domain number (in the DT way) within >> pci_create_host_bridge() too ? > > It is an idea worth pursuing for the 99% of the cases. I would like > to understand the 1% of the time when we want a domain number to be > shared between two host bridges or the time when we want more than > one domain per bridge. Even though we have shared domain, this should be resolved via DT calls, do I miss something ? > > Is that possible? Is it useful? Is it already in practice? This is good question... IMO: 1. Two host bridges can shared domain number if they are children of the same parent host bridge. 2. But I can not find good explanation for more than one domain per bridge. Tomasz