Re: [PATCH] drm/i915: Fix context size calculation on SNB/IVB/VLV

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Aug 22, 2013 at 11:30:55AM -0700, Ben Widawsky wrote:
> On Thu, Aug 22, 2013 at 07:23:13PM +0300, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > All the different context sizes reported in the CXT_SIZE register
> > aren't meant to be simply added together.
> > 
> > While BSpec is somewhat unclear on the topic of the actual context
> > size, empirical tests have now revealed the truth. So let's add a
> > big fat comment to remind people how it all works.
> 
> By the way. I've done some digging. I believe (75% certain) pre-HSW,
> every context save writes the entire data. So if you wanted to set some
> pattern and see what HW actually overwrites, it should be doable. HSW+
> though we can't do that.

Ah right, so you were thinking of initializing the context w/ some
poison, and then see how much is left after the HW has saved. That I
didnb't actually do. Should be reasonable trivial though, so I guess
I'll try it. The same method could also be used to identify whether
HSW skips parts or rearranges the context dynamically.

-- 
Ville Syrjälä
Intel OTC