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

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Message-ID: <CAFCwf10A=-bj2nR8WasNxyQQ07D24Je04tzKxqv2X_XnA0BUSQ@mail.gmail.com>
Date:   Mon, 7 Nov 2022 16:02:01 +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 3:10 PM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Mon, Nov 07, 2022 at 03:01:08PM +0200, Oded Gabbay wrote:
> > 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.
>
> Yeah, I still think this is not the right way, you are getting almost
> nothing from DRM and making everything more complicated in the
> process.
>
> > The only alternative imo to that is to abandon the idea of reusing
> > drm, and just make an independant accel core code.
>
> Not quite really, layer it properly and librarize parts of DRM into
> things accel can re-use so they are not intimately tied to the DRM
> struct device notion.
>
> IMHO this is much better, because accel has very little need of DRM to
> manage a struct device/cdev in the first place.
>
> Jason
I'm not following. How can an accel device be a new type of drm_minor,
if it doesn't have access to all its functions and members ?
How will accel device leverage, for example, the GEM code without
being a drm_minor ?

Librarizing parts of DRM sounds nice in theory but the reality is that
everything there is interconnected, all the structures are
interdependent.
I would have to re-write the entire DRM library to make such a thing
work. I don't think this was the intention.

The current design makes the accel device an integral part of drm,
with very minimal code duplication and without re-writing DRM.

Oded