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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 570ABC31E4A for ; Thu, 13 Jun 2019 17:13:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A09221743 for ; Thu, 13 Jun 2019 17:13:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729110AbfFMRM6 (ORCPT ); Thu, 13 Jun 2019 13:12:58 -0400 Received: from gate.crashing.org ([63.228.1.57]:41808 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728987AbfFLWGA (ORCPT ); Wed, 12 Jun 2019 18:06:00 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x5CM5idM012702; Wed, 12 Jun 2019 17:05:45 -0500 Message-ID: <6f98047e67d16e791ec955db3bc1bc995ee9f16e.camel@kernel.crashing.org> Subject: Re: [PATCH/RESEND] arm64: acpi/pci: invoke _DSM whether to preserve firmware PCI setup From: Benjamin Herrenschmidt To: Lorenzo Pieralisi Cc: Ard Biesheuvel , Bjorn Helgaas , Sinan Kaya , linux-pci , linux-arm-kernel , "Zilberman, Zeev" , "Saidi, Ali" Date: Thu, 13 Jun 2019 08:05:44 +1000 In-Reply-To: <20190612102149.GC6506@redmoon> References: <56715377f941f1953be43b488c2203ec090079a1.camel@kernel.crashing.org> <20190604014945.GE189360@google.com> <960c94eb151ba1d066090774621cf6ca6566d135.camel@kernel.crashing.org> <20190604124959.GF189360@google.com> <4b956e0679b4b4f4d0f0967522590324d15593fb.camel@kernel.crashing.org> <20190611143111.GA11736@redmoon> <20190612102149.GC6506@redmoon> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, 2019-06-12 at 11:21 +0100, Lorenzo Pieralisi wrote: > Hrm. We should probably reassign bus numbers if we reassign resources > > yes, but then I'd like us to not reassign resources unless we have to > > :-) > > But for that we can use _DSM #5 returning 0, at least we would > be consistent. Yes we should be consistent. My personal preference would be to always honor FW resources by default regardless of DSM, and have DSM = 1 force a full reassign instead. In a way, by always reassigning we send the wrong message to FW folks, that it's ok to be broken bcs Linux will fix it up.. Do you know how Windows deals with this ? > Current situation is inconsistent and that bothers me I can put > together a separate patch and send it as an RFT, there are not > that many ARM64 PCI ACPI platforms to test it on. Ok. ../.. > > - pci_read_bridge_bases() is done by pci_bus_claim_resources(), while > > x86 (and powerpc and others) do it in their pcibios_fixup_bus. That one > > is interesting... Any reason why we shouldn't unconditionally read the > > bridges while probing ? Bjorn ? > > I tried and failed miserably: > > https://lore.kernel.org/linux-pci/20150916085850.GA17510@red-moon/ Yes, I see... I think we can revive this if we key it off not reassigning all resources. There's a PCI flag PCI_REASSIGN_ALL_RSRC that's currently only use on powerpc, but it wouldn't be hard to make sure it's set on archs that do a full reassign. We could then have the generic code key off that. That said, I'd rather have this be a host bridge flag. I'll look into it later. > > - When allocating bridge resources, there are interesting differences: > > > > * x86 (and powerpc to some extent): If one has a 0 start or we fail > > to claim it, x86 will wipe out the resource struct (including flags). I > > assume that pci_assign_unassign_* will restore bridges when needed but > > I haven't verified. > > > > * pci_bus_claim_resources() is dumber in that regard. It will call > > pci_claim_bridge_resources() blindly try to claim whatever is there > > even if res->start is 0. This could be a problem with partially > > assigned trees. It also doesn't wipe the resource in case of failure to > > claim which could be a problem going down the tree and letting children > > attach to the non-claimed resource, thus potentially causing the > > reassign pass to fail. > > > > The r->start == 0 test is interesting ... the generic claim code will > > honor IORESOURCE_UNSET but we don't seem to set that generically unless > > we hit some of the specific pass for explicit resource alignment, or > > during the reassignment phases. > > > > - When allocating device resources, the main difference other than the > > 2 passes is that x86 will "0 base" the resource (r->end -= r->start; r- > > > start = 0) for later reassignment. The claim path we use won't do > > > > that. Note: none sets IORESOURCE_UNSET... Additionally x86 has some > > oddball code to save the original FW values and restore them if > > assignment later fails, which is somewhat odd since there's a conflict > > but probably helps really broken setups. > > > > - x86 will not claim ROMs in that pass, it does a 3rd pass just for > > them (it's common I think to not have room for all the ROMs). It also > > disables them in config space during the survey. > > pci_bus_claim_resources() will claim everything and leave ROMs enabled. > > > > So as a somewhat temprary conclusion, I think the main difference here > > is what happens when claim fails (also the res->start = 0 case which we > > need to look at more closely) and whether we should make the generic > > code also "0-base" the resource. > > Oh my, res->start == 0, another can of worms. Honestly I do not know > what to do on that one mostly because we need to figure out how it > plays with resource assignment code (and legacy stuff, you know the > drill). Yes. We have that funny pcibios_uninitialized_bridge_resource() in arch/powerpc/kernel/pci-common.c which tries to "guess" whether a bridge with a 0 res->start means that it's uninitialized or has a "valid" 0 based resource. Among others, we check if memory decoding is enabled, etc... If we decide it's really uninitialized we set IORESOURCE_UNSET, and we rely on that later on. In an idea world, nobody should create valid 0 based resources, it's best to stay off the first 1MB of PCI space due to various legacy concerns anyways but ... > > The question for me really is, do we want to just "upgrade" (if > > necessary) pci_bus_claim_resources() and continue having x86 do its own > > thing for ever, or do we want to consolidate around what is probably > > the most tested platform when it comes to PCI :-) > > Consolidating is the right thing to do, with the caveats above, there > are many but you have all my support. > > > And if we consolidate, I think that won't be by changing what x86 does, > > that code is the result of decades of fiddling to get things right with > > all sorts of broken BIOSes... > > There is 0 chance to change x86 code (and there is 0 chance to change > core PCI code with x86 assumptions in it). I wouldn't say 0 but the bar is high yes. Cheers, Ben.