Re: [Intel-gfx] [PATCH 4/6] drm/i915: Add a struct dma_fence_work timeline

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Wed, 2021-10-13 at 14:43 +0200, Daniel Vetter wrote:
> On Fri, Oct 08, 2021 at 03:35:28PM +0200, Thomas Hellström wrote:
> > The TTM managers and, possibly, the gtt address space managers will
> > need to be able to order fences for async operation.
> > Using dma_fence_is_later() for this will require that the fences we
> > hand
> > them are from a single fence context and ordered.
> > 
> > Introduce a struct dma_fence_work_timeline, and a function to
> > attach
> > struct dma_fence_work to such a timeline in a way that all previous
> > fences attached to the timeline will be signaled when the latest
> > attached struct dma_fence_work signals.
> > 
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> 
> I'm not understanding why we need this:
> 
> - if we just want to order dma_fence work, then an ordered workqueue
> is
>   what we want. Which is why hand-rolling is better than reusing
>   dma_fence_work for absolutely everything.
> 
> - if we just need to make sure the public fences signal in order,
> then
>   it's a dma_fence_chain.

Part of the same series that needs reworking.

What we need here is a way to coalesce multiple fences from various
contexts (including both gpu and work fences) into a single fence and
then attach it to a timeline.

/Thomas