Messages in this thread | | | Date | Thu, 25 Apr 2024 12:59:22 -0600 | Subject | Re: [PATCH] drm/etnaviv: Create an accel device node if compute-only | From | Jeffrey Hugo <> |
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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.
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).
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.
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.
-Jeff
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