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 16:30:45 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Raj, Ashok" <ashok.raj@...el.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>
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 12:23:25PM -0700, Raj, Ashok wrote:
> 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.

It is a different subsystem, different maintainer, and different
reviewers.

It is a development process problem, it doesn't matter what it is
doing.

Jason