[Intel-gfx] [PATCH 4/9] drm/i915: don't update GEN6_PMIMR when it's not needed

[Chris Wilson]

On Wed, Aug 07, 2013 at 10:34:11AM -0300, Paulo Zanoni wrote:
> 2013/8/6 Chris Wilson <chris at chris-wilson.co.uk>:
> > On Tue, Aug 06, 2013 at 06:57:14PM -0300, Paulo Zanoni wrote:
> >> From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> >>
> >> I did some brief tests and the "new_val = pmimr" condition usually
> >> happens a few times after exiting games.
> >>
> >> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> >
> > I'm not sure of the value of this patch by itself. It did make me wonder
> > what you were micro-optimising, and then I saw patch 5 and it made more
> > sense.
> 
> Patches 4 and 5 are just micro optimizations and shouldn't be needed
> for the PC8+, but I thought they would be useful. If you think they're
> not worth it, we can discard them. I was trying to make the code
> similar to the other IMR-changing functions.

Combined together, I think the micro-optimisation makes sense and would
say it was less of a micro-optimisation than a consistent design to use
the bookkeeping instead of touching registers. Just on its own this
patch caused me to do a double-take and question what your motivation
was.
 
> If we massage the code a little bit more we could make all the
> IMR-changing functions share the same code

Sure, that may be worthwhile. Probably borderline though, I envisage it
will take more code to setup than it will save.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre