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

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Date:   Wed, 24 Jul 2019 09:40:04 -0700
From:   Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
To:     Rob Herring <robh@...nel.org>
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

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.

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

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

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