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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxpoj-00049w-VM; Tue, 21 Jul 2020 10:48:14 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxpoh-000499-Hj for linux-arm-kernel@lists.infradead.org; Tue, 21 Jul 2020 10:48:12 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9C364106F; Tue, 21 Jul 2020 03:48:09 -0700 (PDT) Received: from e121166-lin.cambridge.arm.com (e121166-lin.cambridge.arm.com [10.1.196.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2D8533F66E; Tue, 21 Jul 2020 03:48:08 -0700 (PDT) Date: Tue, 21 Jul 2020 11:48:02 +0100 From: Lorenzo Pieralisi To: Pali =?iso-8859-1?Q?Roh=E1r?= Subject: Re: [PATCH v3] PCI: aardvark: Don't touch PCIe registers if no card connected Message-ID: <20200721104802.GA2618@e121166-lin.cambridge.arm.com> References: <20200709113509.GB19638@e121166-lin.cambridge.arm.com> <20200709122208.rmfeuu6zgbwh3fr5@pali> <20200709144701.GA21760@e121166-lin.cambridge.arm.com> <20200709150959.wq6zfkcy4m6hvvpl@pali> <20200710091800.GA3419@e121166-lin.cambridge.arm.com> <20200713082747.e3q3ml3wpbszn4j7@pali> <20200713112325.GA25865@e121166-lin.cambridge.arm.com> <20200715121726.eh4xglkdbcqkh7td@pali> <20200715162108.GB3432@e121166-lin.cambridge.arm.com> <20200721085713.p2rbmucpk5ra3quw@pali> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200721085713.p2rbmucpk5ra3quw@pali> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200721_064811_759315_3301393F X-CRM114-Status: GOOD ( 36.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tomasz Maciej Nowak , linux-pci@vger.kernel.org, Xogium , linux-kernel@vger.kernel.org, Marek =?iso-8859-1?Q?Beh=FAn?= , Remi Pommarel , Thomas Petazzoni , Bjorn Helgaas , linux-arm-kernel@lists.infradead.org, Andrew Murray Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jul 21, 2020 at 10:57:13AM +0200, Pali Roh=E1r wrote: > On Wednesday 15 July 2020 17:21:08 Lorenzo Pieralisi wrote: > > On Wed, Jul 15, 2020 at 02:17:26PM +0200, Pali Roh=E1r wrote: > > > On Monday 13 July 2020 12:23:25 Lorenzo Pieralisi wrote: > > > > On Mon, Jul 13, 2020 at 10:27:47AM +0200, Pali Roh=E1r wrote: > > > > > On Friday 10 July 2020 10:18:00 Lorenzo Pieralisi wrote: > > > > > > On Thu, Jul 09, 2020 at 05:09:59PM +0200, Pali Roh=E1r wrote: > > > > > > > > I understand that but the bridge bus resource can be trimme= d to just > > > > > > > > contain the root bus because that's the only one where ther= e is a > > > > > > > > chance you can enumerate a device. > > > > > > > = > > > > > > > It is possible to register only root bridge without endpoint? > > > > > > = > > > > > > It is possible to register the root bridge with a trimmed IORES= OURCE_BUS > > > > > > so that you don't enumerate anything other than the root port. > > > > > = > > > > > Hello Lorenzo! I really do not know how to achieve it. From code = it > > > > > looks like that pci/probe.c scans child buses unconditionally. > > > > > = > > > > > pci-aardvark.c calls pci_host_probe() which calls functions > > > > > pci_scan_root_bus_bridge() which calls pci_scan_child_bus() which= calls > > > > > pci_scan_child_bus_extend() which calls pci_scan_bridge_extend() = (bridge > > > > > needs to be reconfigured) which then try to probe child bus via > > > > > pci_scan_child_bus_extend() because bridge is not card bus. > > > > > = > > > > > In function pci_scan_bridge_extend() I do not see a way how to sk= ip > > > > > probing for child buses which would avoid enumerating aardvark ro= ot > > > > > bridge when PCIe device is not connected. > > > > > = > > > > > dmesg output contains: > > > > > = > > > > > advk-pcie d0070000.pcie: link never came up > > > > > advk-pcie d0070000.pcie: PCI host bridge to bus 0000:00 > > > > > pci_bus 0000:00: root bus resource [bus 00-ff] > > > > = > > > > This resource can be limited to the root bus number only before cal= ling > > > > pci_host_probe() (ie see pci_parse_request_of_pci_ranges() and code= in > > > > pci_scan_bridge_extend() that programs primary/secondary/subordinate > > > > busses) but I think that only papers over the issue, it does not fi= x it. > > > = > > > I looked at the code in pci/probe.c again and I do not think it is > > > possible to avoid scanning devices. pci_scan_child_bus_extend() is > > > unconditionally calling pci_scan_slot() for devfn=3D0 as the first th= ing. > > > And this function unconditionally calls pci_scan_device() which is > > > directly trying to read vendor id from config register. > > > = > > > So for me it looks like that kernel expects that can read vendor id a= nd > > > device id from config register for device which is not connected. > > = > > Not if it is connected to a bus that the root port does not decode, > > that's what I am saying. > > = > > > And trying to read config register would cause those timeouts in > > > aardvark. > > = > > The root port (which effectively works as PCI bridge from this > > standpoint) does not issue config cycles for busses that aren't within > > its decoded bus range, which in turn is determined by the firmware > > IORESOURCE_BUS resource. > > = > > This issue is caused by devices that are connected downstream to > > the root port. > > = > > Anyway - patch merged > = > Could you send me a link to git commit? I have looked into > lpieralisi/pci.git repository, but I do not see it here. Apologies - I did not push it out, I have pushed it out on pci/aardvark now. > > but I would be happy to keep this discussion going, somehow. > = > Ok, no problem. As I said if anybody has any idea or would like to see > some tests from me, I can do it and provide results. Sounds good, I will let you know, thanks. Lorenzo > > If the LPC20 VFIO/IOMMU/PCI microconference is approved it can be a > > good venue for this to happen. > > = > > Lorenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel