linux-kernel - Re: MSI/MSIX for VFIO platform

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Message-ID: <20200910105735.1e060b95@w520.home>
Date:   Thu, 10 Sep 2020 10:57:35 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Vikas Gupta <vikas.gupta@...adcom.com>
Cc:     Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vikram Prakash <vikram.prakash@...adcom.com>,
        Srinath Mannam <srinath.mannam@...adcom.com>,
        Auger Eric <eric.auger@...hat.com>
Subject: Re: MSI/MSIX for VFIO platform

On Thu, 10 Sep 2020 16:15:27 +0530
Vikas Gupta <vikas.gupta@...adcom.com> wrote:

> Hi Alex/Cornelia,
> 
> We are looking for MSI interrupts for platform devices in user-space
> applications via event/poll mechanism using VFIO.
> 
> Since there is no support for MSI/MSIX handling in VFIO-platform in kernel,
> it may not possible to get this feature in user-space.
> 
> Is there any other way we can get this feature in user-space OR can you
> please suggest if any patch or feature is in progress for same in VFIO
> platform?
> 
> Any suggestions would be helpful.

Eric (Cc'd) is the maintainer of vfio-platform.

vfio-platform devices don't have IRQ indexes dedicated to MSI and MSI-X
like vfio-pci devices do (technically these are PCI concepts, but I
assume we're referring generically to message signaled interrupts), but
that's simply due to the lack of standardization in platform devices.
Logically these are simply collections of edge triggered interrupts,
which the vfio device API supports generically, it's simply a matter
that the vfio bus driver exposing a vfio-platform device create an IRQ
index exposing these vectors.  Thanks,

Alex