[Mesa-dev] [PATCH v2 3/3] i965/gen9: Add workarounds for object preemption.

Kenneth Graunke kenneth at whitecape.org
Wed Oct 31 23:27:31 UTC 2018

On Wednesday, October 31, 2018 11:15:28 AM PDT Rafael Antognolli wrote:
> On Tue, Oct 30, 2018 at 04:32:54PM -0700, Kenneth Graunke wrote:
> > On Monday, October 29, 2018 10:19:54 AM PDT Rafael Antognolli wrote:
> > Do we need any stalling when whacking CS_CHICKEN1...?
> Hmmm... there's this:
> "A fixed function pipe flush is required before modifying this field"
> in the programming notes. I'm not sure what that is, but I assume it's
> some type of PIPE_CONTROL?

Yeah.  I'm not honestly sure what kind - "fixed function pipe flush"
isn't a thing.  Nobody ever uses wording that corresponds to actual
mechanics of the hardware. :(

Maybe this would work:

    brw_emit_end_of_pipe_sync(brw, PIPE_CONTROL_RENDER_TARGET_FLUSH);

> > We may also need to disable autostripping by whacking some chicken
> > registers if it's enabled (Gen9 WA #0799).  Which would be lame,
> Looking again at #0799, it seems it's only applicable up to C0 on SKL,
> and B0 on BXT. So maybe we should be fine here? Or just disable it on
> BXT?

You're right, I misread that.  (I saw the Gen8 "FROM" tag and didn't
notice that it uses "UNTIL" on Gen9...)  Nothing to do here.

> > because that's likely a useful optimization.  I guess we could disable
> > preemption for TRILIST and LINELIST as well to be safe.
> Is this because of the autostripping mentioned above, or some other
> workaround? Or just your impression?
> I can update it to include that, but just want to be sure that it's
> still applicable, once we figure the thing about #0799.

the idea would be to avoid preemption for anything that hits the
autostrip feature.  But, no need, as you noted above.

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