linux-kernel - Re: [RFC KERNEL PATCH v4 3/3] PCI/sysfs: Add gsi sysfs for pci

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Date: Tue, 9 Apr 2024 15:03:14 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Chen, Jiqian" <Jiqian.Chen@....com>,
	"Rafael J . Wysocki" <rafael@...nel.org>
Cc: Roger Pau Monné <roger.pau@...rix.com>,
	Len Brown <lenb@...nel.org>, Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"Hildebrand, Stewart" <Stewart.Hildebrand@....com>,
	"Huang, Ray" <Ray.Huang@....com>
Subject: Re: [RFC KERNEL PATCH v4 3/3] PCI/sysfs: Add gsi sysfs for pci_dev

[+to Rafael]

On Mon, Apr 08, 2024 at 06:42:31AM +0000, Chen, Jiqian wrote:
> Hi Bjorn,
> It has been almost two months since we received your reply last time.
> This series are blocking on this patch, since there are patches on Xen and Qemu side depending on it.
> Do you still have any confusion about this patch? Or do you have other suggestions?
> If no, may I get your Reviewed-by?

  - This is ACPI-specific, but exposes /sys/.../gsi for all systems,
    including non-ACPI systems.  I don't think we want that.

  - Do you care about similar Xen configurations on non-ACPI systems?
    If so, maybe the commit log could mention how you learn about PCI
    INTx routing on them in case there's some way to unify this in the
    future.

  - Missing an update to Documentation/ABI/.

  - A nit: I asked about s/dumU/DomU/ in the commit log earlier,
    haven't seen any response.

  - Commit log mentions "and for other potential scenarios."  It's
    another nit, but unless you have another concrete use for this,
    that phrase is meaningless hand waving and should be dropped.

  - A _PRT entry may refer directly to a GSI or to an interrupt link
    device (PNP0C0F) that can be routed to one of several GSIs:

      ACPI: PCI Interrupt Link [LNKA] (IRQs 3 4 5 6 7 9 10 *11 12 14 15)
 
    I don't think the kernel reconfigures interrupt links after
    enumeration, but if they are reconfigured at run-time (via _SRS),
    the cached GSI will be wrong.  I think setpnp could do this, but
    that tool is dead.  So maybe this isn't a concern anymore, but I
    *would* like to get Rafael's take on this.  If we don't care
    enough, I think we should mention it in the commit log just in
    case.

Bjorn