linux-kernel - Re: [PATCH v4 00/17] Add VFIO mediated device support and DEV-MSI support for the idxd driver

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Date:   Fri, 30 Oct 2020 12:23:25 -0700
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Dave Jiang <dave.jiang@...el.com>, vkoul@...nel.org,
        megha.dey@...el.com, maz@...nel.org, bhelgaas@...gle.com,
        tglx@...utronix.de, alex.williamson@...hat.com,
        jacob.jun.pan@...el.com, yi.l.liu@...el.com, baolu.lu@...el.com,
        kevin.tian@...el.com, sanjay.k.kumar@...el.com,
        tony.luck@...el.com, jing.lin@...el.com, dan.j.williams@...el.com,
        kwankhede@...dia.com, eric.auger@...hat.com, parav@...lanox.com,
        rafael@...nel.org, netanelg@...lanox.com, shahafs@...lanox.com,
        yan.y.zhao@...ux.intel.com, pbonzini@...hat.com,
        samuel.ortiz@...el.com, mona.hossain@...el.com,
        Megha Dey <megha.dey@...ux.intel.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v4 00/17] Add VFIO mediated device support and DEV-MSI
 support for the idxd driver

On Fri, Oct 30, 2020 at 04:17:06PM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 30, 2020 at 12:13:48PM -0700, Dave Jiang wrote:
> > 
> > 
> > On 10/30/2020 11:58 AM, Jason Gunthorpe wrote:
> > > On Fri, Oct 30, 2020 at 11:50:47AM -0700, Dave Jiang wrote:
> > > >   .../ABI/stable/sysfs-driver-dma-idxd          |    6 +
> > > >   Documentation/driver-api/vfio/mdev-idxd.rst   |  404 ++++++
> > > >   MAINTAINERS                                   |    1 +
> > > >   drivers/dma/Kconfig                           |    9 +
> > > >   drivers/dma/idxd/Makefile                     |    2 +
> > > >   drivers/dma/idxd/cdev.c                       |    6 +-
> > > >   drivers/dma/idxd/device.c                     |  294 ++++-
> > > >   drivers/dma/idxd/idxd.h                       |   67 +-
> > > >   drivers/dma/idxd/init.c                       |   86 ++
> > > >   drivers/dma/idxd/irq.c                        |    6 +-
> > > >   drivers/dma/idxd/mdev.c                       | 1121 +++++++++++++++++
> > > >   drivers/dma/idxd/mdev.h                       |  116 ++
> > > 
> > > Again, a subsytem driver belongs in the directory hierarchy of the
> > > subsystem, not in other random places. All this mdev stuff belongs
> > > under drivers/vfio
> > 
> > Alex seems to have disagreed last time....
> > https://lore.kernel.org/dmaengine/20200917113016.425dcde7@x1.home/
> 
> Nobody else in the kernel is splitting subsystems up anymore
>  
> > And I do agree with his perspective. The mdev is an extension of the PF
> > driver. It's a bit awkward to be a stand alone mdev driver under vfio/mdev/.
> 
> By this logic we'd have giagantic drivers under drivers/ethernet
> touching netdev, rdma, scsi, vdpa, etc just because that is where the
> PF driver came from.

What makes you think this is providing services like scsi/rdma/vdpa etc.. ?

for DSA this playes the exact same role, not a different function 
as you highlight above. these mdev's are creating DSA for virtualization
use. They aren't providing a completely different role or subsystem per-se.

Cheers,
Ashok