From: Tomeu Vizoso <tomeu@tomeuvizoso.net>
To: Jeffrey Hugo <quic_jhugo@quicinc.com>
Cc: linux-kernel@vger.kernel.org, Oded Gabbay <ogabbay@kernel.org>,
Lucas Stach <l.stach@pengutronix.de>,
Russell King <linux+etnaviv@armlinux.org.uk>,
Christian Gmeiner <christian.gmeiner@gmail.com>,
David Airlie <airlied@gmail.com>,
Daniel Vetter <daniel@ffwll.ch>,
etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/etnaviv: Create an accel device node if compute-only
Date: Fri, 26 Apr 2024 08:10:02 +0200 [thread overview]
Message-ID: <CAAObsKD4-k7Ya4Mi=vEPaC9DucbnVGDO5SaEUt-_o2_Bg+_FgA@mail.gmail.com> (raw)
In-Reply-To: <8c55dba5-6308-685e-13da-e728197d8101@quicinc.com>
On Thu, Apr 25, 2024 at 8:59 PM Jeffrey Hugo <quic_jhugo@quicinc.com> wrote:
>
> On 4/24/2024 12:37 AM, Tomeu Vizoso wrote:
> > If we expose a render node for NPUs without rendering capabilities, the
> > userspace stack will offer it to compositors and applications for
> > rendering, which of course won't work.
> >
> > Userspace is probably right in not questioning whether a render node
> > might not be capable of supporting rendering, so change it in the kernel
> > instead by exposing a /dev/accel node.
> >
> > Before we bring the device up we don't know whether it is capable of
> > rendering or not (depends on the features of its blocks), so first try
> > to probe a rendering node, and if we find out that there is no rendering
> > hardware, abort and retry with an accel node.
> >
> > Signed-off-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>
> > Cc: Oded Gabbay <ogabbay@kernel.org>
>
> I hope Oded chimes in as Accel maintainer. I think Airlie/Vetter had
> also previously mentioned they'd have opinions on what is Accel vs DRM.
>
> This gets a nack from me in its current state. This is not a strong
> nack, and I don't want to discourage you. I think there is a path forward.
>
> The Accel subsystem documentation says that accel drivers will reside in
> drivers/accel/ but this does not.
Indeed, there is that code organization aspect.
> Also, the commit text for "accel: add dedicated minor for accelerator
> devices" mentions -
>
> "for drivers that
> declare they handle compute accelerator, using a new driver feature
> flag called DRIVER_COMPUTE_ACCEL. It is important to note that this
> driver feature is mutually exclusive with DRIVER_RENDER. Devices that
> want to expose both graphics and compute device char files should be
> handled by two drivers that are connected using the auxiliary bus
> framework."
>
> I don't see any of that happening here (two drivers connected by aux
> bus, one in drivers/accel).
Well, the text refers to devices, not drivers. The case we are talking
about is a driver that wants to sometimes expose an accel node, and
sometimes a render node, depending on the hardware it is dealing with.
So there would either be a device exposing a single render node, or a
device exposing a single accel node.
Though by using the auxiliary bus we could in theory solve the code
organization problem mentioned above, I'm not quite seeing how to do
this in a clean way. The driver in /drivers/gpu/drm would have to be a
DRM driver that doesn't register a DRM device, but registers a device
in the auxiliary bus for the driver in /drivers/accel to bind to? Or
are you seeing some possibility that would fit better in the current
DRM framework?
> I think this is the first case we've had of a combo DRM/Accel usecase,
> and so there isn't an existing example to refer you to on how to
> structure things. I think you are going to be the first example where
> we figure all of this out.
Yep, I will be grateful for any ideas on how to structure this.
> On a more implementation note, ioctls for Accel devices should not be
> marked DRM_RENDER_ALLOW. Seems like your attempt to reuse as much of
> the code as possible trips over this.
Indeed, thanks.
Cheers,
Tomeu
> -Jeff
next prev parent reply other threads:[~2024-04-26 6:10 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 6:37 [PATCH] drm/etnaviv: Create an accel device node if compute-only Tomeu Vizoso
2024-04-25 11:32 ` Christian Gmeiner
2024-04-26 5:36 ` Tomeu Vizoso
2024-04-25 18:59 ` Jeffrey Hugo
2024-04-26 6:10 ` Tomeu Vizoso [this message]
2024-05-09 13:53 ` Tomeu Vizoso
2024-05-09 14:41 ` Oded Gabbay
2024-05-10 8:34 ` Lucas Stach
2024-05-20 7:39 ` Tomeu Vizoso
2024-05-20 11:19 ` Daniel Stone
2024-06-12 14:26 ` Tomeu Vizoso
2024-05-20 9:24 ` Tomeu Vizoso
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