[Intel-gfx] [PATCH 2/2] drm/i915/color: For MTL convert 24 bit lut values to 16 bit

[Borah, Chaitanya Kumar]

Hello Jani,

> -----Original Message-----
> From: Jani Nikula <jani.nikula at linux.intel.com>
> Sent: Monday, June 26, 2023 5:53 PM
> To: Borah, Chaitanya Kumar <chaitanya.kumar.borah at intel.com>; intel-
> gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH 2/2] drm/i915/color: For MTL convert 24 bit lut
> values to 16 bit
> 
> On Mon, 26 Jun 2023, Chaitanya Kumar Borah
> <chaitanya.kumar.borah at intel.com> wrote:
> > For MTL and beyond, convert back the 24 bit lut values read from HW to
> > 16 bit values to maintain parity with userspace values. This way we
> > avoid pipe config mismatch for pre-csc lut values.
> >
> > Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_color.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> > b/drivers/gpu/drm/i915/display/intel_color.c
> > index 25c73e2e6fa3..856191640e71 100644
> > --- a/drivers/gpu/drm/i915/display/intel_color.c
> > +++ b/drivers/gpu/drm/i915/display/intel_color.c
> > @@ -3477,6 +3477,14 @@ static struct drm_property_blob
> *glk_read_degamma_lut(struct intel_crtc *crtc)
> >  	for (i = 0; i < lut_size; i++) {
> >  		u32 val = intel_de_read_fw(dev_priv,
> PRE_CSC_GAMC_DATA(pipe));
> >
> > +		/*
> > +		 * For MTL and beyond, convert back the 24 bit lut values
> > +		 * read from HW to 16 bit values to maintain parity with
> > +		 * userspace values
> > +		 */
> > +		if (DISPLAY_VER(dev_priv) >= 14)
> > +			val = mul_u32_u32(val, (1 << 16)) / (1 << 24);
> > +
> 
> Here too please add a small helper for the conversion.
> 

Thank you for the comment.
I have sent a new version with a helper function. Please let me know if you see any pitfalls with it.

Regards

Chaitanya.

> BR,
> Jani.
> 
> >  		lut[i].red = val;
> >  		lut[i].green = val;
> >  		lut[i].blue = val;
> 
> --
> Jani Nikula, Intel Open Source Graphics Center