[Intel-gfx] [PATCH] drm/i915: Mark hardware context support optional

[Ben Widawsky]

On Tue, 25 Sep 2012 20:41:45 +0100
Chris Wilson <chris at chris-wilson.co.uk> wrote:

> On Tue, 25 Sep 2012 12:04:14 -0700, Ben Widawsky <ben at bwidawsk.net>
> wrote:
> > On Tue, 25 Sep 2012 14:53:37 +0100
> > Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > 
> > > "Enable hardware context support for userspace (default:
> > > disabled))");
> > 
> > You've found one platform this doesn't work on, and a bunch of
> > features rely on this, and yet we default to disabled? That seems a
> > bit harsh to me.
> 
> Exactly, it's meant to be harsh. In the limited testing that hw
> contexts have been exposed to, we have a number of hangs for which
> they are implicated. Therefore they are not safe to enable yet...
> Unless you can prove otherwise. :-p
> -Chris
> 

The reason I've always resisted a module parameter is that rc6 and
contexts are tied so very closely together. We've had a number of
issues around rc6 already, I do not want contexts to be conflated with
those issues. It's interesting if rc6=0 and failures still occur. I've
yet to hear of such an issue, but I'd like to know if that's the case
here.

As a side note, I'll mention yet again that we're missing a workaround
which Daniel (and I believe you as well) have previously
preemptively shot down involving sending a 3d primitive down the pipe
at certain times. IIRC those are only required with rc6 enabled.

Also, AFAIK many HW problems are fixed in IVB, and even more fixed in
HSW, so disabling for all platforms seems like not the right decision
to me. At least, as long as we only have evidence of one failing
platform.

As mesa will depend on this feature more and more, and with no error
state or other info to go on, again I think we should defer globally
disabling until we get more info, or else we risk not getting more info.

-- 
Ben Widawsky, Intel Open Source Technology Center