A sequence like:
1) set_framebuffer_state(A)
2) clears and/or draws
3) set_framebuffer_state(B)
4) context_flush(ASYNC)
would result in the fence for batch B being returned, instead of batch A.
Resulting in a fence that signals too early.
Instead, in context_flush() find the most recently modified batch, so
that in the example above batch A would be flushed.
There is one wrinkle, that we want to avoid a dependency loop. So the
'last_batch' can actually be a batch that depends on the most recently
modified batch. But in either case, the batch that is used for the
returned fence is one that directly or indirectly depends on all other
batches associated with the context.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30064>
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