Re: [PATCH 10/10] drm/i915: remove "unclaimed register" checks from I915_WRITE

[Chris Wilson <chris@chris-wilson.co.uk>]

On Fri, 18 Jan 2013 12:49:13 -0800, Ben Widawsky <ben@bwidawsk.net> wrote:
> On Fri, Jan 18, 2013 at 06:29:12PM -0200, Paulo Zanoni wrote:
> > From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > 
> > Some developers don't really like this code polluting I915_WRITE, and
> > we've never really measured its negative impacts. So now that we
> > properly print ERR_INT interrupts, let's remove the I915_WRITE code
> > and promote the interrupt error message to DRM_ERROR.
> > 
> > The downside of this change is that we lose the ability to check the
> > register and print nice backtraces, but at this point most of the
> > errors have already been fixed and we're investigating the few
> > remaining cases.
> > 
> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> 
> I'm really sad to see this go. Especially since our time between new
> platform bring-up is decreasing so much. If I were to guess right, every
> developer working on a new platform would want this. So while HSW may be
> in the clear, HSW+1 suffers.

I don't like the extra work per iowrite32, but I can live with for the
error-detection. I would rather remove it for special cases where it has
demonstrable impact, perhaps in execbuffer. However, you can equally lay
the blame there for execbuffer hitting i915_write32 too often. So even
there I am not convinced that speeding up i915_write32 is the best
approach.

So NAKed-by: Chris Wilson <chris@chris-wilson.co.uk> unless you can find
a way to work out the faulting register address in the interrupt or that
is the only method going forward.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre