From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Date: Thu, 13 Apr 2017 10:42:58 +0100 From: Lorenzo Pieralisi To: Ard Biesheuvel Subject: Re: [PATCH 1/2] drivers: pci: do not disregard parent resources starting at 0x0 Message-ID: <20170413094258.GA12432@red-moon> References: <20170411163313.18577-1-ard.biesheuvel@linaro.org> <20170411163313.18577-2-ard.biesheuvel@linaro.org> <20170412132423.GA6584@red-moon> MIME-Version: 1.0 In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , Graeme Gregory , linux-pci , Will Deacon , Leif Lindholm , Sinan Kaya , Tomasz Nowicki , Bjorn Helgaas , Yinghai Lu , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+bjorn=helgaas.com@lists.infradead.org List-ID: On Thu, Apr 13, 2017 at 08:39:12AM +0100, Ard Biesheuvel wrote: > On 12 April 2017 at 14:24, Lorenzo Pieralisi wrote: > > [+Yinghai, Bjorn] > > > > On Tue, Apr 11, 2017 at 05:33:12PM +0100, Ard Biesheuvel wrote: > >> Commit f44116ae8818 ("PCI: Remove pci_find_parent_resource() use for > >> allocation") updated the logic that iterates over all bus resources > >> and compares them to a given resource, in order to decide whether one > >> is the parent of the latter. > >> > >> This change inadvertently causes pci_find_parent_resource() to disregard > >> resources starting at address 0x0, resulting in an error such as the one > >> below on ARM systems whose I/O window starts at 0x0. > >> > >> pci_bus 0000:00: root bus resource [mem 0x10000000-0x3efeffff window] > >> pci_bus 0000:00: root bus resource [io 0x0000-0xffff window] > >> pci_bus 0000:00: root bus resource [mem 0x8000000000-0xffffffffff window] > >> pci_bus 0000:00: root bus resource [bus 00-0f] > >> pci 0000:00:01.0: PCI bridge to [bus 01] > >> pci 0000:00:02.0: PCI bridge to [bus 02] > >> pci 0000:00:03.0: PCI bridge to [bus 03] > >> pci 0000:00:03.0: can't claim BAR 13 [io 0x0000-0x0fff]: no compatible bridge window > >> pci 0000:03:01.0: can't claim BAR 0 [io 0x0000-0x001f]: no compatible bridge window > >> > >> While this never happens on x86, it is perfectly legal in general for a > >> PCI MMIO or IO window to start at address 0x0, and it was supported in > >> the code before commit f44116ae8818. > >> > >> So let's drop the test for res->start != 0; resource_contains() already > >> checks whether [start, end) completely covers the resource, and so it > >> should be redundant. > >> > >> Fixes: f44116ae8818 ("PCI: Remove pci_find_parent_resource() use for allocation") > > > > I know this code fixes IO claiming on ARM/ARM64 (well, it fixes nothing > > because we never claim resources on ARM/ARM64 apart from kvmtool and > > generic host bridge), my _big_ worry is that it can cause endless > > regressions on other arches, in any case I would be really really > > careful about adding a Fixes: tag to it. > > > > The patch is only 3 years old, and is obviously a regression given > that the change in behavior described here occurs as a side effect. I agree with you that res->start usage changed with f44116ae8818 but I am not sure you can call that a regression unless we prove there was some code relying on the previous behaviour (and it is not just x86). Anyway, I am happy to put these two patches (with some tweaks on patch 2) on a branch for testing on ARM64 ACPI platforms to see the best way forward. Thanks, Lorenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel