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 16:17:06 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Dave Jiang <dave.jiang@...el.com>
CC:     <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>,
        <ashok.raj@...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 12:13:48PM -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.

It is not how the kernel works. Subsystem owners are responsible for
their subsystem, drivers implementing their subsystem are under the
subsystem directory.

Jason