On Tue, May 12, 2020 at 4:14 AM Dave Airlie <airlied@xxxxxxxxx> wrote: > > On Mon, 11 May 2020 at 19:37, Oded Gabbay <oded.gabbay@xxxxxxxxx> wrote: > > > > On Mon, May 11, 2020 at 12:11 PM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > > > > > > It's the default. > > Thanks for catching that. > > > > > > > > Also so much for "we're not going to tell the graphics people how to > > > review their code", dma_fence is a pretty core piece of gpu driver > > > infrastructure. And it's very much uapi relevant, including piles of > > > corresponding userspace protocols and libraries for how to pass these > > > around. > > > > > > Would be great if habanalabs would not use this (from a quick look > > > it's not needed at all), since open source the userspace and playing > > > by the usual rules isn't on the table. If that's not possible (because > > > it's actually using the uapi part of dma_fence to interact with gpu > > > drivers) then we have exactly what everyone promised we'd want to > > > avoid. > > > > We don't use the uapi parts, we currently only using the fencing and > > signaling ability of this module inside our kernel code. But maybe I > > didn't understand what you request. You want us *not* to use this > > well-written piece of kernel code because it is only used by graphics > > drivers ? > > I'm sorry but I don't get this argument, if this is indeed what you meant. > > We would rather drivers using a feature that has requirements on > correct userspace implementations of the feature have a userspace that > is open source and auditable. > > Fencing is tricky, cross-device fencing is really tricky, and having > the ability for a closed userspace component to mess up other people's > drivers, think i915 shared with closed habana userspace and shared > fences, decreases ability to debug things. > > Ideally we wouldn't offer users known untested/broken scenarios, so > yes we'd prefer that drivers that intend to expose a userspace fencing > api around dma-fence would adhere to the rules of the gpu drivers. > > I'm not say you have to drop using dma-fence, but if you move towards > cross-device stuff I believe other drivers would be correct in > refusing to interact with fences from here. The flip side is if you only used dma-fence.c "because it's there", and not because it comes with an uapi attached and a cross-driver kernel internal contract for how to interact with gpu drivers, then there's really not much point in using it. It's a custom-rolled wait_queue/event thing, that's all. Without the gpu uapi and gpu cross-driver contract it would be much cleaner to just use wait_queue directly, and that's a construct all kernel developers understand, not just gpu folks. From a quick look at least habanalabs doesn't use any of these uapi/cross-driver/gpu bits. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch
