linux-kernel - Re: [patch RFC 26/38] x86/xen: Wrap XEN MSI management into irqdomain

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Message-ID: <87r1rv5f9j.fsf@nanos.tec.linutronix.de>
Date:   Tue, 25 Aug 2020 09:57:44 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jürgen Groß <jgross@...e.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, linux-pci@...r.kernel.org,
        xen-devel@...ts.xenproject.org, Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Jon Derrick <jonathan.derrick@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Wei Liu <wei.liu@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <rja@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Megha Dey <megha.dey@...el.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Baolu Lu <baolu.lu@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch RFC 26/38] x86/xen: Wrap XEN MSI management into irqdomain

On Mon, Aug 24 2020 at 08:21, Jürgen Groß wrote:
> On 21.08.20 02:24, Thomas Gleixner wrote:
>
> Looking into https://www.kernel.org/doc/Documentation/IRQ-domain.txt (is
> this still valid?)

It's halfways correct. Emphasis on halfways.

> I believe Xen should be able to use the "No Map" approach, as Xen only
> ever uses software IRQs (at least those are the only ones visible to
> any driver). The (virtualized) hardware interrupts are Xen events
> after all.
>
> So maybe morphing Xen into supporting irqdomains in a sane way isn't
> that complicated. Maybe I'm missing the main complexities, though.

The wrapper domain I did is pretty much that, but with the extra
functionality required by hierarchical irq domains. So, yes it's
functionally correct, but it's only utilizing the alloc/free interface
and not any of the other mechanisms provided by irqdomains. The latter
should make the overall code simpler but that obviously needs some
thought.

Thanks,

        tglx