From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bjorn Helgaas Subject: Re: [RFC PATCH] PCI/portdrv: Support for subtractive decode bridge Date: Thu, 7 Feb 2019 13:52:30 -0600 Message-ID: <20190207195230.GJ7268@google.com> References: <1544758829-10327-1-git-send-email-honghui.zhang@mediatek.com> <20190207151816.GI7268@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190207151816.GI7268@google.com> Sender: linux-kernel-owner@vger.kernel.org To: honghui.zhang@mediatek.com Cc: youlin.pei@mediatek.com, lorenzo.pieralisi@arm.com, poza@codeaurora.org, fred@fredlawl.com, linux-pci@vger.kernel.org, rafael.j.wysocki@intel.com, linux-kernel@vger.kernel.org, jianjun.wang@mediatek.com, ryder.lee@mediatek.com, linux-mediatek@lists.infradead.org, matthias.bgg@gmail.com, linux-arm-kernel@lists.infradead.org List-Id: linux-mediatek@lists.infradead.org On Thu, Feb 07, 2019 at 09:18:16AM -0600, Bjorn Helgaas wrote: > On Fri, Dec 14, 2018 at 11:40:29AM +0800, honghui.zhang@mediatek.com wrote: > > From: Honghui Zhang > > > > The Class Code for subtractive decode PCI-to-PCI bridge is 060401h, > > change the class_mask values to make portdrv support this type bridge. > > I assume you have a Root Port or Switch Port that supports subtractive > decode? I'm trying to understand how such a device would work. > > Out of curiosity, can you show the "lspci -vv" output for the device > and the downstream devices of interest? Actually, since subtractive decode has to do with how the bridge interacts with its *peers*, what would be interesting is the host bridge window information from ACPI _CRS or DT and the lspci info for everything under that host bridge. Assuming we're talking about a Root Port, I guess that would mean anything inside the host bridge windows but outside the positive decode windows (the normal PCI-PCI bridge apertures in the Root Ports) would be claimed by the subtractive decode Root Port? I guess you would want this because this path ultimately leads to an ISA or similar bus where you don't know what resources the device actually consumes? Bjorn