Re: [RFC KERNEL PATCH v4 3/3] PCI/sysfs: Add gsi sysfs for pci_dev

[Bjorn Helgaas <helgaas@kernel.org>]

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?