linux-kernel - Re: [PATCH] drm/panfrost: Export all GPU feature registers

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Message-ID: <CAL_Jsq+cLg5R=SJ0zjfVqYB_So-gHT3qb16wcOCbrHuufSZgLw@mail.gmail.com>
Date:   Wed, 24 Jul 2019 10:45:11 -0600
From:   Rob Herring <robh@...nel.org>
To:     Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Cc:     Steven Price <steven.price@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>
Subject: Re: [PATCH] drm/panfrost: Export all GPU feature registers

On Wed, Jul 24, 2019 at 10:40 AM Alyssa Rosenzweig
<alyssa.rosenzweig@...labora.com> wrote:
>
> This is definitely helpful!
>
> My one concern is, supposing userspace really does need all of this
> information, is it wasteful to have to do 30+ ioctls just to get this?
> kbase had a single ioctl to grab all of the properties, whether
> userspace wanted them or not. I'm not sure if that's better -- the two
> approaches are rather polar opposites.

I think this ship already sailed when we added the first one with
GPU_ID. Also, at least etnaviv works the same way.

>
> Granted this would be on driver init so not a critical path.

Exactly.

>
> On Wed, Jul 24, 2019 at 10:27:03AM -0600, Rob Herring wrote:
> > Adding Alyssa's Collabora email.
> >
> > On Wed, Jul 24, 2019 at 4:56 AM Steven Price <steven.price@....com> wrote:
> > >
> > > Midgard/Bifrost GPUs have a bunch of feature registers providing details
> > > of what the hardware supports. Panfrost already reads these, this patch
> > > exports them all to user space so that the jobs created by the user space
> > > driver can be tuned for the particular hardware implementation.
> > >
> > > Signed-off-by: Steven Price <steven.price@....com>
> > > ---
> > >  drivers/gpu/drm/panfrost/panfrost_device.h |  1 +
> > >  drivers/gpu/drm/panfrost/panfrost_drv.c    | 38 +++++++++++++++++++--
> > >  drivers/gpu/drm/panfrost/panfrost_gpu.c    |  2 ++
> > >  include/uapi/drm/panfrost_drm.h            | 39 ++++++++++++++++++++++
> > >  4 files changed, 77 insertions(+), 3 deletions(-)
> >
> > LGTM. I'll give it a bit more time to see if there are any comments
> > before I apply it.
> >
> > Rob