From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from quartz.orcorp.ca ([184.70.90.242]:34761 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754877Ab3A1WJE (ORCPT ); Mon, 28 Jan 2013 17:09:04 -0500 Date: Mon, 28 Jan 2013 15:09:04 -0700 From: Jason Gunthorpe To: Stephen Warren Cc: Arnd Bergmann , Thomas Petazzoni , Bjorn Helgaas , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jason Cooper , Andrew Lunn , Gregory Clement , Maen Suleiman , Lior Amsalem , Thierry Reding , Eran Ben-Avi , Nadav Haklai , Shadi Ammouri , Tawfik Bayouk , Russell King - ARM Linux Subject: Re: [PATCH v2 07/27] PCI: Add software-emulated host bridge Message-ID: <20130128220904.GA21446@obsidianresearch.com> References: <1359399397-29729-1-git-send-email-thomas.petazzoni@free-electrons.com> <1359399397-29729-8-git-send-email-thomas.petazzoni@free-electrons.com> <201301282018.17714.arnd@arndb.de> <5106F5CB.8050304@wwwdotorg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <5106F5CB.8050304@wwwdotorg.org> Sender: linux-pci-owner@vger.kernel.org List-ID: On Mon, Jan 28, 2013 at 03:03:55PM -0700, Stephen Warren wrote: > On 01/28/2013 01:18 PM, Arnd Bergmann wrote: > > On Monday 28 January 2013, Thomas Petazzoni wrote: > >> From: Thierry Reding > >> > >> [Thomas Petazzoni: > >> - Simplify capabilities handling. > >> - Move to a separate file. > >> - Fix mask used when writing a 4 bytes value.] > >> > >> Signed-off-by: Thierry Reding > >> Signed-off-by: Thomas Petazzoni > > > > Not even a description why this is needed? > > > > This patch (together with patch 8) seems like the most controversial > > one of the series, so you should better provide a really good reason > > why we would emulate something in software rather than using whatever > > hardware is there. > > At least on Tegra, there is no HW that exposes PCI configuration > registers for the host bridge itself. Only the root ports have exposed > PCI configuration registers. There was some debate re: whether a host > bridge device needed to exist or not. This patch makes such a device > exist if it's required. If Linux will discover properly (I strongly suspect it does) without the host bridge, then I would say to ditch this... The PCI-E standard requires a host bridge device, but if Linux doesn't require it then there is no reason to emulate one. That would simplify the question of PCI IDs - for Marvell's case and the sw root port bridge we can just copy the IDs from the bogus config space of the HW. Jason