drm/scheduler for vc5

Eric Anholt eric at anholt.net
Fri Mar 30 20:05:22 UTC 2018

I've been keeping my eye on what's going on with drm/scheduler, and I'm
definitely interested in using it.  I've got some questions about how to
fit it to this HW, though.

For this HW, most rendering jobs have two phases: binning and rendering,
and the HW has two small FIFOs for descriptions of each type of job to
be submitted.  The bin portion must be completed before emitting the
render.  Some jobs may be render only, skipping the bin phase.

The render side is what takes most of the time.  However, you can
usually bin the next frame while rendering the current one, helping keep
your shared shader cores busy when you're parsing command lists.  The
exception is if the next bin depends on your last render (think
render-to-texture with texturing in a vertex shader).

This makes me think that I should expose two entities for the HW's
binner and the renderer.  Each VC6 job would have two drm_sched_job: The
render job would depend on the fence from the bin job, and bin may or
may not depend on the previous render.

However, as an extra complication, the MMU is shared between binner and
renderer, so I can't schedule a new job with a page table change until
the other side finishes up.  Is there a good way to express this with
drm/scheduler, or should I work around this by internally stalling my
job submissions to the HW when a page table change is needed, and then
trigger that page table swap and submit once a job completes?
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