linux-kernel - Re: [tip:x86/platform] x86/PCI/mmcfg: Switch to ECAM config mode if possible

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Message-ID: <20170630183057.GA27351@mail.rc.ru>
Date:   Fri, 30 Jun 2017 19:30:57 +0100
From:   Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Yinghai Lu <yinghai@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Matthew Wilcox <willy@...ux.intel.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/platform] x86/PCI/mmcfg: Switch to ECAM config mode if
 possible

On Fri, Jun 30, 2017 at 10:16:15AM -0700, Linus Torvalds wrote:
> On Fri, Jun 30, 2017 at 7:30 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >> But MCFG problems were a long time ago and noone uses these systems anymore,
> >> so perhaps he is right.
> >
> > The obvious solution to this is to force type 1 for older machines, i.e. <=
> > K8. Some day we should stop supporting 15+ years old crap just because we
> > can.
> 
> No.
> 
> The fact is, type 1 is the *good* thing.  It's the standard thing that
> has worked pretty much forever, and that is not just tested, but has
> good semantics.

Fully agreed.

Also, config space accesses supposed to be *safe* rather than *fast*.

There was quite a heated discussion on this very subject back in 2008.
Thought that I have a full copy of that, but no, surprisingly...
Google still gives a sufficient part of that:

http://linux-kernel.2935.n7.nabble.com/Patch-v2-Make-PCI-extended-config-space-MMCONFIG-a-driver-opt-in-td243861i60.html

Ivan.