linux-kernel - Re: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV

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Message-ID: <87d03x5x0k.fsf@nanos.tec.linutronix.de>
Date:   Tue, 11 Aug 2020 11:53:31 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Dey\, Megha" <megha.dey@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        "gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     Marc Zyngier <maz@...nel.org>,
        "Jiang\, Dave" <dave.jiang@...el.com>,
        "vkoul\@kernel.org" <vkoul@...nel.org>,
        "bhelgaas\@google.com" <bhelgaas@...gle.com>,
        "rafael\@kernel.org" <rafael@...nel.org>,
        "hpa\@zytor.com" <hpa@...or.com>,
        "alex.williamson\@redhat.com" <alex.williamson@...hat.com>,
        "Pan\, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj\, Ashok" <ashok.raj@...el.com>,
        "Liu\, Yi L" <yi.l.liu@...el.com>,
        "Lu\, Baolu" <baolu.lu@...el.com>,
        "Tian\, Kevin" <kevin.tian@...el.com>,
        "Kumar\, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Luck\, Tony" <tony.luck@...el.com>,
        "Lin\, Jing" <jing.lin@...el.com>,
        "Williams\, Dan J" <dan.j.williams@...el.com>,
        "kwankhede\@nvidia.com" <kwankhede@...dia.com>,
        "eric.auger\@redhat.com" <eric.auger@...hat.com>,
        "parav\@mellanox.com" <parav@...lanox.com>,
        "Hansen\, Dave" <dave.hansen@...el.com>,
        "netanelg\@mellanox.com" <netanelg@...lanox.com>,
        "shahafs\@mellanox.com" <shahafs@...lanox.com>,
        "yan.y.zhao\@linux.intel.com" <yan.y.zhao@...ux.intel.com>,
        "pbonzini\@redhat.com" <pbonzini@...hat.com>,
        "Ortiz\, Samuel" <samuel.ortiz@...el.com>,
        "Hossain\, Mona" <mona.hossain@...el.com>,
        "dmaengine\@vger.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86\@kernel.org" <x86@...nel.org>,
        "linux-pci\@vger.kernel.org" <linux-pci@...r.kernel.org>,
        "kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
        xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI irq domain

Thomas Gleixner <tglx@...utronix.de> writes:

CC+: XEN folks

> Thomas Gleixner <tglx@...utronix.de> writes:
>> The infrastructure itself is not more than a thin wrapper around the
>> existing msi domain infrastructure and might even share code with
>> platform-msi.
>
> And the annoying fact that you need XEN support which opens another can
> of worms...

which needs some real cleanup first.

x86 still does not associate the irq domain to devices at device
discovery time, i.e. the device::msi_domain pointer is never populated.

So to support this new fangled device MSI stuff we'd need yet more
x86/xen specific arch_*msi_irqs() indirection and hackery, which is not
going to happen.

The right thing to do is to convert XEN MSI support over to proper irq
domains. This allows to populate device::msi_domain which makes a lot of
things simpler and also more consistent.

Thanks,

        tglx