drm/i915: Add support for CHV pipe B sprite CSC

drm/i915: Add support for CHV pipe B sprite CSC

CHV has a programmable CSC unit on the pipe B sprites. Program the unit
appropriately for BT.601 limited range YCbCr to full range RGB color
conversion. This matches the programming we currently do for sprites
on the other pipes and on other platforms.

It seems the CSC only works when the input data is YCbCr. For RGB
pixel formats it doesn't matter what we program into the CSC registers.
Doesn't make much sense to me especially since the register names give
the impression that RGB input data would also work. But that's how
it behaves here.

In the review discussions there's been some nice math to explain the
values obtained here. First about the YCbCr->RGB matrix:

"I had the RGB->YCbCr matrix, inverted it and the values came out. But they
should match the wikipedia article. Also keep in mind that the coefficients
are in .12 in fixed point format, hence we need a 1<<12 factor. So let's
try it:

Kb=.114
Kr=.299
(1<<12) * 255/219 ~= 4769
-(1<<12) * 255/112*(1-Kb)*Kb/(1-Kb-Kr) ~= -1605
-(1<<12) * 255/112*(1-Kr)*Kr/(1-Kb-Kr) ~= -3330
(1<<12) * 255/112*(1-Kr) ~= 6537
(1<<12) * 255/112*(1-Kb) ~= 8263

"Looks like the same values to me."

And then about the limits used for clamping:

"> where did you get these min/max?

"The hardware apparently deals in 10bit values, so we need to multiply everything
by 4 when we start with the 8bit min/max values.

Y = [16:235] * 4 = [64:940]
CbCr = ([16:240] - 128) * 4 = [-112:112] * 4 = [-448:448]

"The -128 being the -0.5 bias that the hardware already applied before
the data entered the CSC unit."

Raw data is also supplied in 10bpc in the registers.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by Rodrigo Vivi <rodrigo.vivi@intel.com>
[danvet: Copypaste explanations&math from the review discussion.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>