From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 46167C3499A for ; Fri, 13 Dec 2019 20:37:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B4CD24776 for ; Fri, 13 Dec 2019 20:37:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727711AbfLMOjm (ORCPT ); Fri, 13 Dec 2019 09:39:42 -0500 Received: from foss.arm.com ([217.140.110.172]:33340 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727673AbfLMOjm (ORCPT ); Fri, 13 Dec 2019 09:39:42 -0500 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 03CA31435; Fri, 13 Dec 2019 06:39:41 -0800 (PST) Received: from donnerap.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 808A73F52E; Fri, 13 Dec 2019 06:39:39 -0800 (PST) Date: Fri, 13 Dec 2019 14:39:36 +0000 From: Andre Przywara To: Andrew Murray Cc: Bjorn Helgaas , Lorenzo Pieralisi , "Rafael J . Wysocki" , Len Brown , Will Deacon , Catalin Marinas , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org Subject: Re: [PATCH] pcie: Add quirk for the Arm Neoverse N1SDP platform Message-ID: <20191213143936.2160dd9d@donnerap.cambridge.arm.com> In-Reply-To: <20191212210723.GJ24359@e119886-lin.cambridge.arm.com> References: <20191209160638.141431-1-andre.przywara@arm.com> <20191210144115.GA94877@google.com> <20191212210723.GJ24359@e119886-lin.cambridge.arm.com> Organization: ARM X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; aarch64-unknown-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, 12 Dec 2019 21:07:24 +0000 Andrew Murray wrote: Hi, > On Tue, Dec 10, 2019 at 08:41:15AM -0600, Bjorn Helgaas wrote: > > On Mon, Dec 09, 2019 at 04:06:38PM +0000, Andre Przywara wrote: [ ... ] > > Even ECAM compliance is not really minor -- if this controller were > > fully compliant with the spec, you would need ZERO Linux changes to > > support it. Every quirk like this means additional maintenance > > burden, and it's not just a one-time thing. It means old kernels that > > *should* "just work" on your system will not work unless somebody > > backports the quirk. > > With regards to URs resulting in unwanted aborts or similar - this seems > to be a very common theme amongst ARM PCI controller drivers. For example > both ARM32 imx6 and ARM32 keystone have fault handlers to handle an abort > and fabricate a 0xffffffff read value. > > The ARM32 rcar driver, whilst it doesn't appear to produce an abort, does > read the PCI_STATUS register after making a config read to determine if > any aborts have happened - in which case it reports > PCIBIOS_DEVICE_NOT_FOUND. > > And as recently reported [1], the rockchip driver also appears to produce > aborts. > > I suspect that this ARM64 controller driver won't be the last either. Thus > any solution here may form the basis of copy-cat solutions for subsequent > controllers. Well, I think Bjorn is aware of them, but was actually hoping that those broken controllers would go away at some point ;-) And just to make this clear: I would categorise this issue as an integration bug, which just can't be fixed in hardware or firmware easily. It was never meant to be this way. So I am not sure we should promote generic solutions here. > From my understanding of the issues, the ARM64 serrors are imprecise and > as a result there isn't a sensible way of using them to determine that a > read is a UR. So where there are no other solutions to suppress the > generation of an abort by the controller, the only solutions that seem to > exist are 1) pre-scan the devices in firmware and only talk to those devices > in Linux - a safe option but limiting - perhaps with side effects for CRS > and 2) the approach rcar takes in using the PCI_STATUS register - though > you'd end up having to mask the serror (PSTATE.A) for a limited period of > time - a risky option (you'll miss real serrors) - but with no side effects. > > (I don't know if option 2 is feasible in this case by the way). Interesting, we might evaluate this, but mostly out of curiosity or for debugging. I don't think it's really a better option. If there is a safe way of making this work in the majority of cases, that should be the way to go. Setting PSTATE.A sounds quite wacky to me. Thanks, Andre. > [1] https://lore.kernel.org/linux-pci/2a381384-9d47-a7e2-679c-780950cd862d@rock-chips.com/2-0001-WFT-PCI-rockchip-play-game-with-unsupported-request-.patch > > Thanks, > > Andrew Murray > > > > > > This allows the Arm Neoverse N1SDP board to boot Linux without crashing > > > and to access *any* devices (there are no platform devices except UART).