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

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Message-ID: <CAPj87rPnA1eKR_b7gAhDiMZRcVt8xPS9xnsscqVQ_a_qO_tD4A@mail.gmail.com>
Date: Wed, 26 Jun 2024 20:26:04 +0100
From: Daniel Stone <daniel@...ishbar.org>
To: Daniel Stone <daniel@...ishbar.org>, Lucas Stach <l.stach@...gutronix.de>, 
	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>
Cc: Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/etnaviv: Create an accel device node if compute-only

On Wed, 26 Jun 2024 at 18:52, Daniel Vetter <daniel@...ll.ch> wrote:
> On Wed, Jun 26, 2024 at 11:39:01AM +0100, Daniel Stone wrote:
> > On Wed, 26 Jun 2024 at 09:28, Lucas Stach <l.stach@...gutronix.de> wrote:
> > > 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.
>
> Yeah mesa sounds kinda broken here ...
>
> What might work in the kernel is if you publish a fake 3d engine that's
> too new for broken mesa, if that's enough to make it fail to bind? And if
> mesa still happily binds against that, then yeah it's probably too broken
> and we need etnaviv-v2 (as a drm driver uapi name, I think that's what
> mesa filters?) for anything new (including the NN-only ones).
>
> I would still try to avoid that, but just in case someone screams about
> regressions.

It's not just etnaviv, it's literally every Mesa driver which works
with decoupled render/display. So that would be etnaviv-v2,
panfrost-v2, panthor-v2, v3d-v2, powervr-v2, ... albeit those don't
tend to have multiple instances.

Anyway, I'm still leaning towards the answer being: this is not an
etnaviv regression caused by NPU, it's a longstanding generic Mesa
issue for which the answer is to fix the known fragility.

Cheers,
Daniel