linux-kernel - Re: [RFC PATCH v2 1/3] drivers/accel: define kconfig and register a new major

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Message-ID: <CAFCwf10K-dTu455QfOK8i6thismY-FUN2Rws830EGiqOcGWFgA@mail.gmail.com>
Date:   Mon, 7 Nov 2022 15:01:08 +0200
From:   Oded Gabbay <ogabbay@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Arnd Bergmann <arnd@...db.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        John Hubbard <jhubbard@...dia.com>,
        Alex Deucher <alexander.deucher@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
        Jiho Chu <jiho.chu@...sung.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
        Maciej Kwapulinski <maciej.kwapulinski@...ux.intel.com>,
        stanislaw.gruszka@...el.com
Subject: Re: [RFC PATCH v2 1/3] drivers/accel: define kconfig and register a
 new major

On Mon, Nov 7, 2022 at 2:56 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Thu, Nov 03, 2022 at 10:39:36PM +0200, Oded Gabbay wrote:
> > On Thu, Nov 3, 2022 at 3:31 PM Oded Gabbay <ogabbay@...nel.org> wrote:
> > >
> > > On Thu, Nov 3, 2022 at 2:31 AM Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > On Wed, Nov 02, 2022 at 10:34:03PM +0200, Oded Gabbay wrote:
> > > > > --- /dev/null
> > > > > +++ b/drivers/accel/Kconfig
> > > > > @@ -0,0 +1,24 @@
> > > > > +# SPDX-License-Identifier: GPL-2.0-only
> > > > > +#
> > > > > +# Compute Acceleration device configuration
> > > > > +#
> > > > > +# This framework provides support for compute acceleration devices, such
> > > > > +# as, but not limited to, Machine-Learning and Deep-Learning acceleration
> > > > > +# devices
> > > > > +#
> > > > > +menuconfig ACCEL
> > > > > +     tristate "Compute Acceleration Framework"
> > > > > +     depends on DRM
> > > > > +     help
> > > > > +       Framework for device drivers of compute acceleration devices, such
> > > > > +       as, but not limited to, Machine-Learning and Deep-Learning
> > > > > +       acceleration devices.
> > > > > +       If you say Y here, you need to select the module that's right for
> > > > > +       your acceleration device from the list below.
> > > > > +       This framework is integrated with the DRM subsystem as compute
> > > > > +       accelerators and GPUs share a lot in common and can use almost the
> > > > > +       same infrastructure code.
> > > > > +       Having said that, acceleration devices will have a different
> > > > > +       major number than GPUs, and will be exposed to user-space using
> > > > > +       different device files, called accel/accel* (in /dev, sysfs
> > > > > +       and debugfs)
> > > >
> > > > Module name if "M" is chosen?
> > > Will add
> > So, unfortunately, the path of doing accel as a kernel module won't
> > work cleanly (Thanks stanislaw for pointing this out to me).
> > The reason is the circular dependency between drm and accel. drm calls
> > accel exported symbols during init and when devices are registering
> > (all the minor handling), and accel calls drm exported symbols because
> > I don't want to duplicate the entire drm core code.
>
> I really don't think this is the right way to integrate with
> DRM. Accel should be a layer over top of DRM, not have these wakky
> co-dependencies.
>
> The fact you are running into stuff like this already smells really
> bad.
>
> Jason
I don't agree with your statement that it should be "a layer over top of DRM".
Anything on top of DRM is a device driver.
Accel is not a device driver, it is a new type of drm minor / drm driver.

Please look at v3 of the patch-set. There I abandoned the idea of
having accel as a separate module and instead it is part of drm.ko, as
it should be because it is just a new drm minor.

The only alternative imo to that is to abandon the idea of reusing
drm, and just make an independant accel core code.

Oded