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

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Message-ID: <CAJZ5v0hr12dZig=A1sDyDhFN32Yn05Vxd=+q6TuVgzVwurrjsg@mail.gmail.com>
Date: Wed, 7 Jan 2026 19:13:58 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Haakon Bugge <haakon.bugge@...cle.com>
Cc: 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>, 
	"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>, Lukas Wunner <lukas@...ner.de>, 
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: Re: [PATCH] PCI/ACPI: Do not fiddle with ExtTag and RO in program_hpx_type2

On Wed, Jan 7, 2026 at 6:59 PM Haakon Bugge <haakon.bugge@...cle.com> wrote:
>
> >
> >
> >> 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.

And I'm still hoping to receive some feedback from the PCI side on this.

Thanks!