linux-kernel - Re: [PATCH v2 1/1] PCI: Add Extended Tag + MRRS quirk for Xeon 6

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Message-ID: <6808171089b0f_71fe294d0@dwillia2-xfh.jf.intel.com.notmuch>
Date: Tue, 22 Apr 2025 15:24:16 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Bjorn Helgaas <helgaas@...nel.org>, Ilpo Järvinen
	<ilpo.jarvinen@...ux.intel.com>
CC: Dan Williams <dan.j.williams@...el.com>, Lukas Wunner <lukas@...ner.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>, <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] PCI: Add Extended Tag + MRRS quirk for Xeon 6

Bjorn Helgaas wrote:
[..]
> v1/rfc: https://lore.kernel.org/all/20250304135108.2599-1-ilpo.jarvinen@linux.intel.com/
> 
> I suppose it's quixotic to hope for anything better than quirks that
> have to be added or updated for every new processor that comes along.
> 
> ACPI _HPX might be a possible way for the platform to tell us what to
> do here.  ACPI r6.5, sec 6.2.9 says it's for hot-added devices and
> "Functions not configured by the platform firmware during initial
> system boot" (how are we supposed to determine that?)  In any case,
> Linux does evaluate _HPX for every device in pci_configure_device().
> 
> I'm not sure _HPX really works; it's very general, and I would expect
> to see reports of problems if firmware really tried to use it.
> 
> Or, I guess a _DSM function would be a possible way to communicate
> this.

Ok, I am reading this as "Maintainer asserts the quirk is unsavory,
please make this be something that Linux can ask the platform firmware
if it needs to apply, or make existing _HPX just work. Either of those
is preferable to a new entry in the quirk table."