Re: [PATCH] drm/i915: Implement pipe CSC based limited range RGB output

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

On Fri, Jan 18, 2013 at 07:11:38PM +0200, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> HSW no longer has the PIPECONF bit for limited range RGB output.
> Instead the pipe CSC unit must be used to perform that task.
> 
> The CSC pre offset are set to 0, since the incoming data is full
> [0:255] range RGB, the coefficients are programmed to compress the
> data into [0:219] range, and then we use either the CSC_MODE black
> screen offset bit, or the CSC post offsets to shift the data to
> the correct [16:235] range.
> 
> Also have to change the confiuration of all planes so that the
> data is sent through the pipe CSC unit. For simplicity send the
> plane data through the pipe CSC unit always, and in case full
> range output is requested, the pipe CSC unit is set up with an
> identity transform to pass the plane data through unchanged.
> 
> I've been told by some hardware people that the use of the pipe
> CSC unit shouldn't result in any measurable increase in power
> consumption numbers.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
> Note that I haven't actually tested this on HSW. I did test the earlier
> prototype version on ILK and IVB. The pipe CSC unit on ILK isn't programmed
> in quite the same as on HSW, but the IVB unit _should_ be identical to HSW.
> 
> The main risk involves the coefficient registers. If the channel mapping
> changed for some reason, we could get swapped channels. For some reason
> reality and documenation didn't seem to agree how the channels are mapped
> even on ILK and IVB. So I'd like someone to try this out on HSW to make
> sure the output still looks correct.

FYI I just tested this on a HSW box, and all the colors look correct.
I also verified that the pipeconf color range bit is well and truly gone
(hw won't allow you to even set it).

So Daniel, I think this can go in as is.

-- 
Ville Syrjälä
Intel OTC