Re: [PATCH v3] drm: Add UAPI for the Asahi driver

[Alyssa Rosenzweig <alyssa@rosenzweig.io>]

> >>>> +    /** 
> >>>> +     * @DRM_ASAHI_BIND_SINGLE_PAGE: Map a single page of the BO repeatedly 
> >>>> +     * across the VA range. 
> >>>> +     * 
> >>>> +     * This is useful to fill a VA range with scratch pages or zero pages. 
> >>>> +     * It is intended as a mechanism to accelerate sparse. 
> >>>> +     */ 
> >>>> +    DRM_ASAHI_BIND_SINGLE_PAGE = (1L << 2),
> >> 
> >> Does this require the BO to be a single page? If so, does it require offset==0? Or does it just take whatever page is at the specified offset?
> > 
> > I believe the intention is that it takes whatever page is at the
> > specified offset and just maps that a bunch of times. HK doesn't use
> > this yet though it probably should (this was added to help reduce
> > overhead when emulating sparse with scratch/zero pages, which is still
> > very new functionality in hk).
> > 
> > Accelerating this properly involves GPUVM patches - although even without
> > that, moving the loop into the kernel so it's only a single ioctl
> > (user-kernel roundtrip) seems worth keeping the flag for.
> 
> FYI: I will be posting a patch for the GPUVM abstraction soon.

Great to hear :) Although in this case, I meant that accelerating
DRM_ASAHI_BIND_SINGLE_PAGE requires patches to extend the actual C
implementation of drm/gpuvm, not just the Rust abstraction. Which is a
bit annoying for non-essential functionality with regards to upstreaming
things...