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

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Message-ID: <20240123160252.GA316914@bhelgaas>
Date: Tue, 23 Jan 2024 10:02:52 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Chen, Jiqian" <Jiqian.Chen@....com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, 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>,
	Roger Pau Monné <roger.pau@...rix.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>,
	"Ragiadakou, Xenia" <Xenia.Ragiadakou@....com>
Subject: Re: [RFC KERNEL PATCH v4 3/3] PCI/sysfs: Add gsi sysfs for pci_dev

On Tue, Jan 23, 2024 at 10:13:52AM +0000, Chen, Jiqian wrote:
> On 2024/1/23 07:37, Bjorn Helgaas wrote:
> > On Fri, Jan 05, 2024 at 02:22:17PM +0800, Jiqian Chen wrote:
> >> There is a need for some scenarios to use gsi sysfs.
> >> For example, when xen passthrough a device to dumU, it will
> >> use gsi to map pirq, but currently userspace can't get gsi
> >> number.
> >> So, add gsi sysfs for that and for other potential scenarios.
> ...

> > I don't know enough about Xen to know why it needs the GSI in
> > userspace.  Is this passthrough brand new functionality that can't be
> > done today because we don't expose the GSI yet?
>
> In Xen architecture, there is a privileged domain named Dom0 that
> has ACPI support and is responsible for detecting and controlling
> the hardware, also it performs privileged operations such as the
> creation of normal (unprivileged) domains DomUs. When we give to a
> DomU direct access to a device, we need also to route the physical
> interrupts to the DomU. In order to do so Xen needs to setup and map
> the interrupts appropriately.

What kernel interfaces are used for this setup and mapping?