[Intel-gfx] [PATCH] drm/i915: Add OACONTROL to the command parser register whitelist.

[Jesse Barnes]

On Thu, 27 Mar 2014 16:22:44 -0700
Kenneth Graunke <kenneth at whitecape.org> wrote:

> On 03/27/2014 03:44 PM, Daniel Vetter wrote:
> > On Thu, Mar 27, 2014 at 10:34 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> >> Why are we parsing batches with I915_EXEC_SECURE at all?  Secure batches
> >> are only issued from trusted code which is guaranteed to be running as
> >> root.  I don't see any benefit to scanning those batches, and there's
> >> definitely overhead.
> >>
> >> I mean, sure, it may be reasonable in the short term as a way to test
> >> the command parser, but I certainly hope we don't *ship* that.
> > 
> > Everyone runs X as root, but I kinda want X to also be able to run as
> > non-root. The cmd parser has a special list of drm master register
> > lists which should allow this, but if we just bypass the cmd parser
> > for all normal X installs we'll have 0 test coverage on this. Which
> > means broken like hell.
> > 
> > Hence I actually intend to ship this, yes. Chris doesn't like it either really.
> > -Daniel
> 
> Seriously?  Hurt performance on every user's system just so you can test
> things?  That a classic case of the tail wagging the dog.
> 
> Why not make a i915.enable_cmd_parser=2 value which enables it all the
> time and use that when running igt?  Clearly being able to test this is
> valuable, but enabling it universally is *not* OK.

Daniel, I'm not sure what you mean by 0 coverage.  Surely DRI clients
count for something?  And X shouldn't be submitting all its batches
with the secure bit set, right?  If so, we ought to fix that and only
use it for ones where it's necessary (e.g. wait events or similar).  I
agree with Ken and Chris here.

Chris?

-- 
Jesse Barnes, Intel Open Source Technology Center