linux-kernel - Re: [PATCH] PCI/ACPI: Do not fiddle with ExtTag and RO in program_hpx

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Message-ID: <1C290028-E094-48E3-B2CC-29734CEBC97C@oracle.com>
Date: Wed, 7 Jan 2026 17:58:14 +0000
From: Haakon Bugge <haakon.bugge@...cle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Sinan Kaya <okaya@...eaurora.org>,
        Casey
 Leedom <leedom@...lsio.com>, Ashok Raj <ashok.raj@...el.com>,
        "David S.
 Miller" <davem@...emloft.net>,
        dingtianhong <dingtianhong@...wei.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>
CC: "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI/ACPI: Do not fiddle with ExtTag and RO in
 program_hpx_type2

> 
> 
>> On 5 Dec 2025, at 13:28, Håkon Bugge <Haakon.Bugge@...cle.com> wrote:
>> 
>> After commit 60db3a4d8cc9 ("PCI: Enable PCIe Extended Tags if
>> supported"), the kernel controls enablement of extended tags
>> (ExtTag). Similar, after commit a99b646afa8a ("PCI: Disable PCIe
>> Relaxed Ordering if unsupported"), the kernel controls the relaxed
>> ordering bit (RO), in the sense that the kernel keeps the bit set (if
>> already set) unless the RC does not support it.
>> 
>> On some platforms, when program_hpx_type2() is called and the _HPX
>> object's Type2 records are, let's say, dubious, we may end up
>> resetting ExtTag and RO, although they were explicit set or kept set
>> by the OSPM [1].
>> 
>> The Advanced Configuration and Power Interface (ACPI) Specification
>> version 6.6 has a provision that gives the OSPM the ability to
>> control these bits any way. In a note in section 6.2.9, it is stated:
>> 
>> "OSPM may override the settings provided by the _HPX object's Type2
>> record (PCI Express Settings) or Type3 record (PCI Express Descriptor
>> Settings) when OSPM has assumed native control of the corresponding
>> feature."
>> 
>> So, in order to preserve the increased performance of ExtTag and RO on
>> platforms that support any of these, we make sure program_hpx_type2()
>> doesn't reset them.
>> 
>> [1] Operating System-directed configuration and Power Management
>> 
>> Fixes: 60db3a4d8cc9 ("PCI: Enable PCIe Extended Tags if supported")
>> Fixes: a99b646afa8a ("PCI: Disable PCIe Relaxed Ordering if unsupported")
>> Signed-off-by: Håkon Bugge <haakon.bugge@...cle.com>
> 
> A gentle ping on this one.

And a re-ping.


Thxs, Håkon


> 
> Thxs, Håkon