[PATCH 2/4] drm/i915: Adjust LUT rounding rules

[Ville Syrjälä]

On Mon, Nov 20, 2023 at 06:08:57AM +0000, Borah, Chaitanya Kumar wrote:
> Hello Ville,
> 
> > -----Original Message-----
> > From: dri-devel <dri-devel-bounces at lists.freedesktop.org> On Behalf Of Ville
> > Syrjala
> > Sent: Friday, October 13, 2023 6:44 PM
> > To: intel-gfx at lists.freedesktop.org
> > Cc: dri-devel at lists.freedesktop.org
> > Subject: [PATCH 2/4] drm/i915: Adjust LUT rounding rules
> > 
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > drm_color_lut_extract() rounding was changed to follow the OpenGL int<-
> > >float conversion rules. Adjust intel_color_lut_pack() to match.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_color.c | 14 ++++++--------
> >  1 file changed, 6 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> > b/drivers/gpu/drm/i915/display/intel_color.c
> > index 2a2a163ea652..b01f463af861 100644
> > --- a/drivers/gpu/drm/i915/display/intel_color.c
> > +++ b/drivers/gpu/drm/i915/display/intel_color.c
> > @@ -785,14 +785,12 @@ static void chv_assign_csc(struct intel_crtc_state
> > *crtc_state)
> >  /* convert hw value with given bit_precision to lut property val */  static u32
> > intel_color_lut_pack(u32 val, int bit_precision)  {
> 
> Is this operation unique to Intel. Should there be a drm helper for this?

If some other driver gains gamma readout support they
could probably use something like this. The other option
would be to rework the current helper to allow conversions
both ways.

> 
> Regards
> 
> Chaitanya
> 
> > -	u32 max = 0xffff >> (16 - bit_precision);
> > -
> > -	val = clamp_val(val, 0, max);
> > -
> > -	if (bit_precision < 16)
> > -		val <<= 16 - bit_precision;
> > -
> > -	return val;
> > +	if (bit_precision > 16)
> > +		return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(val, (1 << 16)
> > - 1),
> > +					     (1 << bit_precision) - 1);
> > +	else
> > +		return DIV_ROUND_CLOSEST(val * ((1 << 16) - 1),
> > +					 (1 << bit_precision) - 1);
> >  }
> > 
> >  static u32 i9xx_lut_8(const struct drm_color_lut *color)
> > --
> > 2.41.0
> 

-- 
Ville Syrjälä
Intel