linux-kernel - Re: Bug report: the extended PCI config space is missed with 6.2-rc2

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Message-ID: <63b7289cb7439_5174129445@dwillia2-xfh.jf.intel.com.notmuch>
Date:   Thu, 5 Jan 2023 11:44:28 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        "Luck, Tony" <tony.luck@...el.com>
CC:     "Liang, Kan" <kan.liang@...ux.intel.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "kernelorg@...ead.fr" <kernelorg@...ead.fr>,
        "kjhambrick@...il.com" <kjhambrick@...il.com>,
        "2lprbe78@...k.com" <2lprbe78@...k.com>,
        "nicholas.johnson-opensource@...look.com.au" 
        <nicholas.johnson-opensource@...look.com.au>,
        "benoitg@...us.ca" <benoitg@...us.ca>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "wse@...edocomputers.com" <wse@...edocomputers.com>,
        "mumblingdrunkard@...tonmail.com" <mumblingdrunkard@...tonmail.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Box, David E" <david.e.box@...el.com>,
        "Sun, Yunying" <yunying.sun@...el.com>
Subject: Re: Bug report: the extended PCI config space is missed with 6.2-rc2

Bjorn Helgaas wrote:
> On Thu, Jan 05, 2023 at 06:04:52PM +0000, Luck, Tony wrote:
> > > Hi Tony, can you share a dmesg log?  Does it look like the same thing
> > > Kan reported, where the ECAM space is reported only via an
> > > EfiMemoryMappedIO region and is not otherwise reserved by firmware?
> > 
> > Attached are serial logs. "broken" is the one from v6.2-rc2, "revert" is the
> > one with your commit reverted.
> > 
> > I don't see the string "ECAM" in either of them.
> 
> Yeah, "ECAM" is what the PCIe spec calls it, but Linux logging uses
> "MMCONFIG".  Probably should change that.
> 
> Anyway, your dmesg log shows the same problem:
> 
>   DMI: Intel Corporation BRICKLAND/BRICKLAND, BIOS BRBDXSD1.86B.0338.V01.1603162127 03/16/2016
>   efi: Remove mem48: MMIO range=[0x80000000-0x8fffffff] (256MB) from e820 map
>   PCI: MMCONFIG for domain 0000 [bus 00-ff] at [mem 0x80000000-0x8fffffff] (base 0x80000000)
>   [Firmware Info]: PCI: MMCONFIG at [mem 0x80000000-0x8fffffff] not reserved in ACPI motherboard resources
>   PCI: not using MMCONFIG
>   acpi PNP0A03:00: fail to add MMCONFIG information, can't access extended configuration space under this bridge
> 
> Apparently the only mention of [mem 0x80000000-0x8fffffff] in the
> firmware/kernel interface is as an EfiMemoryMappedIO region.
> 
> I think this is a firmware bug, but obviously we're going to have to
> figure out a way around it.

Definitely an ambiguity / conflict, but not sure it is a bug when you
look at from the perspective of how would an EFI runtime service use
ECAM/MMCONFIG space? 

Would it be enough to add this clarification in "EFI 2.9 Table 7-6
Memory Type Usage after ExitBootServices()"?

s/This memory is not used by the OS./This memory is not used by the OS,
unless ACPI declares it for another puporse./