linux-kernel - Re: [PATCH] drm/etnaviv: Create an accel device node if compute-only

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Date: Wed, 26 Jun 2024 11:39:01 +0100
From: Daniel Stone <daniel@...ishbar.org>
To: Lucas Stach <l.stach@...gutronix.de>
Cc: Daniel Vetter <daniel@...ll.ch>, Tomeu Vizoso <tomeu@...euvizoso.net>, linux-kernel@...r.kernel.org, 
	Oded Gabbay <ogabbay@...nel.org>, Russell King <linux+etnaviv@...linux.org.uk>, 
	Christian Gmeiner <christian.gmeiner@...il.com>, David Airlie <airlied@...il.com>, 
	etnaviv@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
	Daniel Stone <daniels@...labora.com>
Subject: Re: [PATCH] drm/etnaviv: Create an accel device node if compute-only

Hi,

On Wed, 26 Jun 2024 at 09:28, Lucas Stach <l.stach@...gutronix.de> wrote:
> Mesa doesn't cope right now. Mostly because of the renderonly thing
> where we magically need to match render devices to otherwise render
> incapable KMS devices. The way this matching works is that the
> renderonly code tries to open a screen on a rendernode and if that
> succeeds we treat it as the matching render device.
>
> The core of the issue is that we have no way of specifying which kind
> of screen we need at that point, i.e. if the screen should have 3D
> render capabilities or if compute-only or even NN-accel-only would be
> okay. So we can't fail screen creation if there is no 3D engine, as
> this would break the teflon case, which needs a screen for the NN
> accel, but once we successfully create a screen reanderonly might treat
> the thing as a rendering device.
> So we are kind of stuck here between breaking one or the other use-
> case. I'm leaning heavily into the direction of just fixing Mesa, so we
> can specify the type of screen we need at creation time to avoid the
> renderonly issue, porting this change as far back as reasonably
> possible and file old userspace into shit-happens.

Yeah, honestly this sounds like the best solution to me too.

Cheers,
Daniel