linux-kernel - RE: RESEND: MMCONFIG related question

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Message-ID: <SJ0PR11MB674419202D61518CB81282DD92C19@SJ0PR11MB6744.namprd11.prod.outlook.com>
Date:   Mon, 16 Jan 2023 01:53:45 +0000
From:   "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yang, Lixiao" <lixiao.yang@...el.com>,
        "Peng, Chao P" <chao.p.peng@...el.com>
Subject: RE: RESEND: MMCONFIG related question



>-----Original Message-----
>From: Bjorn Helgaas <helgaas@...nel.org>
>Sent: Friday, January 13, 2023 9:54 PM
>To: Duan, Zhenzhong <zhenzhong.duan@...el.com>
>Cc: bhelgaas@...gle.com; linux-kernel@...r.kernel.org; Yang, Lixiao
><lixiao.yang@...el.com>; Peng, Chao P <chao.p.peng@...el.com>
>Subject: Re: RESEND: MMCONFIG related question
>
>On Fri, Jan 13, 2023 at 10:15:45AM +0000, Duan, Zhenzhong wrote:
>> Recently Lixiao reported sriov disappered for cards which supported
>> sriov. We found it's related to commit "07eab0901ed efi/x86: Remove
>> EfiMemoryMappedIO from E820 map" which removed
>EfiMemoryMappedIO
>> regions from E820 map which lead to pci_mmcfg_reject_broken() check
>> failed, raw_pci_ext_ops isn't set to pci_mmcfg finally, below is the
>> related log. I know maybe bios should add MMCONFIG region into ACPI
>> motherboard resources, just want to ask if we would support the case
>> when MMCONFIG is missed in ACPI motherboard resources as I see it's
>> treated as "Firmware Info" not "Firmware bug". Thanks
>
>The patches here:
>https://lore.kernel.org/linux-pci/20230110180243.1590045-1-
>helgaas@...nel.org/
>should resolve this problem.
Will try.

>
>> Also has another question, if MMCONFIG happened to be in
>> EfiMemoryMappedIO, even if it's removed from E820 map so that there is
>> no CRS clip for that region, could it be used for BAR space?
>
>MMCONFIG cannot be used for BAR space.  MMCONFIG should be reported
>via PNP0C02 _CRS.  BAR space, i.e., a PCI host bridge aperture, should be
>reported via PNP0A03 _CRS.
>
>> Will there be conflict for BAR and MMCONFIG access?
>
>I don't think so, but I don't completely understand the scenario you're asking
>about.
I mean the case when MMCONFIG space reported by ACPI table overlap with PCI host bridge aperture reported by PNP0A03 _CRS. Just realized this case should be firmware bug, sorry for confusing.

>
>The E820 clipping of PCI host bridge windows is only intended to work around
>an issue where PNP0A03 _CRS reports space that is not part of the host bridge
>windows.  E.g., there were a few platforms that seemed to report host bridge
>register space via _CRS.
Understood, thanks Bjorn.