Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig

From	Bjorn Helgaas <helgaas@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig
Date	2017-03-14 20:50 +0100
Message-ID	<tl0Ce-4V8-13@gated-at.bofh.it> (permalink)
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On Tue, Mar 14, 2017 at 06:56:26PM +0100, Thomas Gleixner wrote:
> On Tue, 14 Mar 2017, Andi Kleen wrote:
> > The other option is to simply make it unconditional. That would
> > be even simpler, but it is a bit more risky. Hmm, I suppose may
> > be worth trying to find out what Windows uses. If they get away
> > with MMCONFIG everywhere we should be too.
> 
> From the PCIe spec:
> 
>  The PCI 3.0 compatible Configuration Space can be accessed using either
>  the mechanism defined in the PCI Local Bus Specification or the PCI
>  Express Enhanced Configuration Access Mechanism (ECAM) described later in
>  this section. Accesses made using either access mechanism are
>  equivalent. The PCI Express Extended Configuration Space can only be
>  accessed by using the ECAM.
> 
> The 1.0 spec has a similar wording (s/3.0/2.3).
> 
> Definitely the best way to go.

I agree that it should be fairly safe to do ECAM/MMCONFIG without
locking.  Can we handle the decision part by adding a "lockless" bit
to struct pci_ops?  Old ops don't mention that bit, so it will be
initialized to zero and we'll do locking as today.  ECAM/MMCONFIG ops
can set it and we can skip the locking.

Bjorn

Thread

Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Thomas Gleixner <tglx@linutronix.de> - 2017-03-14 15:00 +0100
  Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Andi Kleen <ak@linux.intel.com> - 2017-03-14 16:50 +0100
    Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Thomas Gleixner <tglx@linutronix.de> - 2017-03-14 17:50 +0100
      Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Andi Kleen <ak@linux.intel.com> - 2017-03-14 18:10 +0100
        Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Thomas Gleixner <tglx@linutronix.de> - 2017-03-14 19:00 +0100
          Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Bjorn Helgaas <helgaas@kernel.org> - 2017-03-14 20:50 +0100
            Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Andi Kleen <andi@firstfloor.org> - 2017-03-15 03:30 +0100
              Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Bjorn Helgaas <helgaas@kernel.org> - 2017-03-15 04:00 +0100
                Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Thomas Gleixner <tglx@linutronix.de> - 2017-03-15 11:10 +0100
                Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Bjorn Helgaas <helgaas@kernel.org> - 2017-03-15 15:20 +0100
                Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Andi Kleen <andi@firstfloor.org> - 2017-03-16 01:10 +0100
                Re: [PATCH 3/4] x86, pci: Add interface to force mmconfig Thomas Gleixner <tglx@linutronix.de> - 2017-03-16 23:50 +0100

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