[Mesa-dev] [PATCH 09/10] i965/meta: Remove fast_clear_color variable

[Ben Widawsky]

On Wed, Oct 14, 2015 at 08:16:54AM -0700, Ben Widawsky wrote:
> On Wed, Oct 14, 2015 at 11:52:03AM +0200, Neil Roberts wrote:
> > This patch doesn't look right. See this sentence in “Render Target Fast
> > Clear”:
> > 
> > “The pixel shader kernel requires no attributes, and delivers a value of
> >  0xFFFFFFFF in all channels of the render target write message”
> > 
> > Presumably the fast_clear_color is trying to implement this restriction.
> > 
> > Regards,
> > - Neil
> > 
> 
> You're right. Originally the patch only touched the color in the resolve pass,
> which I believe doesn't matter (nor does the actual shader we bind). However,
> I'm sort of baffled now why I'd see no piglit regressions since the clear color
> will *never* be all F.
> 
> Either way, I'll drop this patch - but my confusion level has increased.
> 

Ah. I remember why I did this. I was following this from the spec:
"SW does not need to compile any PS for clear and resolve passes but must ensure
that PS dispatch enable bit is set."

Note that is specifically says, "clear". Kristian and I had some theory that
GEN9 has some magic way of clearing the MCS without using the shader, and that
was where this idea came from. Note that I don't believe this is actually true,
and I have dropped the patch.

[snip]