Re: [PATCH] PCI/ACPI: Do not fiddle with ExtTag and RO in program_hpx_type2

Haakon Bugge
2026-01-07T17:59:15Z

>
>
>> On 5 Dec 2025, at 13:28, Håkon Bugge <Haakon.Bugge@oracle.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@oracle.com>
>
> A gentle ping on this one.

And a re-ping.

Thxs, Håkon

>
> Thxs, Håkon