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

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Message-ID: <8a8a853c-cbe6-b19c-f6ba-c8cdeda84a36@intel.com>
Date:   Tue, 11 Aug 2020 11:46:10 -0700
From:   "Dey, Megha" <megha.dey@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...dia.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     Marc Zyngier <maz@...nel.org>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "alex.williamson@...hat.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>,
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        "Hossain, Mona" <mona.hossain@...el.com>,
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        <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

Hi Thomas,

On 8/11/2020 2:53 AM, Thomas Gleixner wrote:
> 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...

hmm I am not sure why we need Xen support... are you referring to idxd 
using xen?

> 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.

do you think this cleanup is to be a precursor to my patches? I could 
look into it but I am not familiar with the background of Xen

and this stuff. Can you please provide further guidance on where to look?

> Thanks,
>
>          tglx