Re: [Intel-gfx] [PATCH 11/11] drm/i915: Create resized LUTs for ivb+ split gamma mode

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

On Fri, Nov 04, 2022 at 10:49:39AM +0530, Nautiyal, Ankit K wrote:
> Patch looks good to me.
> 
> Minor suggestions inline:
> 
> On 10/26/2022 5:09 PM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Currently when opeating in split gamma mode we do the
> nitpick: 'operating' typo.
> > "skip ever other sw LUT entry" trick in the low level
> > LUT programming/readout functions. That is very annoying
> > and a big hinderance to revamping the color management
> > uapi.
> >
> > Let's get rid of that problem by making half sized copies
> > of the software LUTs and plugging those into the internal
> > {pre,post}_csc_lut attachment points (instead of the sticking
> > the uapi provide sw LUTs there directly).
> >
> > With this the low level stuff will operate purely in terms
> > the hardware LUT sizes, and all uapi nonsense is contained
> > to the atomic check phase. The one thing we do lose is
> > intel_color_assert_luts() since we no longer have a way to
> > check that the uapi LUTs were correctly used when generating
> > the internal copies. But that seems like a price worth paying.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/display/intel_color.c | 81 +++++++++++++++++-----
> >   1 file changed, 64 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_color.c b/drivers/gpu/drm/i915/display/intel_color.c
> > index 33871bfacee7..d48904f90e3a 100644
> > --- a/drivers/gpu/drm/i915/display/intel_color.c
> > +++ b/drivers/gpu/drm/i915/display/intel_color.c
> > @@ -597,6 +597,30 @@ create_linear_lut(struct drm_i915_private *i915, int lut_size)
> >   	return blob;
> >   }
> >   
> > +static struct drm_property_blob *
> > +create_resized_lut(struct drm_i915_private *i915,
> > +		   const struct drm_property_blob *blob_in, int lut_out_size)
> > +{
> > +	int i, lut_in_size = drm_color_lut_size(blob_in);
> > +	struct drm_property_blob *blob_out;
> > +	const struct drm_color_lut *lut_in;
> > +	struct drm_color_lut *lut_out;
> > +
> > +	blob_out = drm_property_create_blob(&i915->drm,
> > +					    sizeof(lut_out[0]) * lut_out_size,
> > +					    NULL);
> > +	if (IS_ERR(blob_out))
> > +		return blob_out;
> > +
> > +	lut_in = blob_in->data;
> > +	lut_out = blob_out->data;
> > +
> > +	for (i = 0; i < lut_out_size; i++)
> > +		lut_out[i] = lut_in[i * (lut_in_size - 1) / (lut_out_size - 1)];
> > +
> > +	return blob_out;
> > +}
> > +
> >   static void i9xx_load_lut_8(struct intel_crtc *crtc,
> >   			    const struct drm_property_blob *blob)
> >   {
> > @@ -723,19 +747,14 @@ static void ivb_load_lut_10(struct intel_crtc *crtc,
> >   			    u32 prec_index)
> >   {
> >   	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
> > -	int hw_lut_size = ivb_lut_10_size(prec_index);
> >   	const struct drm_color_lut *lut = blob->data;
> >   	int i, lut_size = drm_color_lut_size(blob);
> >   	enum pipe pipe = crtc->pipe;
> >   
> > -	for (i = 0; i < hw_lut_size; i++) {
> > -		/* We discard half the user entries in split gamma mode */
> > -		const struct drm_color_lut *entry =
> > -			&lut[i * (lut_size - 1) / (hw_lut_size - 1)];
> > -
> > +	for (i = 0; i < lut_size; i++) {
> >   		intel_de_write_fw(i915, PREC_PAL_INDEX(pipe), prec_index++);
> >   		intel_de_write_fw(i915, PREC_PAL_DATA(pipe),
> > -				  ilk_lut_10(entry));
> > +				  ilk_lut_10(&lut[i]));
> >   	}
> >   
> >   	/*
> > @@ -751,7 +770,6 @@ static void bdw_load_lut_10(struct intel_crtc *crtc,
> >   			    u32 prec_index)
> >   {
> >   	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
> > -	int hw_lut_size = ivb_lut_10_size(prec_index);
> >   	const struct drm_color_lut *lut = blob->data;
> >   	int i, lut_size = drm_color_lut_size(blob);
> >   	enum pipe pipe = crtc->pipe;
> > @@ -759,14 +777,9 @@ static void bdw_load_lut_10(struct intel_crtc *crtc,
> >   	intel_de_write_fw(i915, PREC_PAL_INDEX(pipe),
> >   			  prec_index | PAL_PREC_AUTO_INCREMENT);
> >   
> > -	for (i = 0; i < hw_lut_size; i++) {
> > -		/* We discard half the user entries in split gamma mode */
> > -		const struct drm_color_lut *entry =
> > -			&lut[i * (lut_size - 1) / (hw_lut_size - 1)];
> > -
> > +	for (i = 0; i < lut_size; i++)
> >   		intel_de_write_fw(i915, PREC_PAL_DATA(pipe),
> > -				  ilk_lut_10(entry));
> > -	}
> > +				  ilk_lut_10(&lut[i]));
> >   
> >   	/*
> >   	 * Reset the index, otherwise it prevents the legacy palette to be
> > @@ -1343,7 +1356,7 @@ void intel_color_assert_luts(const struct intel_crtc_state *crtc_state)
> >   			    crtc_state->pre_csc_lut != i915->display.color.glk_linear_degamma_lut);
> >   		drm_WARN_ON(&i915->drm,
> >   			    crtc_state->post_csc_lut != crtc_state->hw.gamma_lut);
> > -	} else {
> > +	} else if (crtc_state->gamma_mode != GAMMA_MODE_MODE_SPLIT) {
> >   		drm_WARN_ON(&i915->drm,
> >   			    crtc_state->pre_csc_lut != crtc_state->hw.degamma_lut &&
> >   			    crtc_state->pre_csc_lut != crtc_state->hw.gamma_lut);
> > @@ -1564,6 +1577,38 @@ static u32 ivb_csc_mode(const struct intel_crtc_state *crtc_state)
> >   	return CSC_POSITION_BEFORE_GAMMA;
> >   }
> >   
> > +static int ivb_assign_luts(struct intel_crtc_state *crtc_state)
> > +{
> > +	struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
> > +	struct drm_property_blob *degamma_lut, *gamma_lut;
> > +
> > +	if (crtc_state->gamma_mode != GAMMA_MODE_MODE_SPLIT) {
> > +		ilk_assign_luts(crtc_state);
> > +		return 0;
> > +	}
> > +
> > +	drm_WARN_ON(&i915->drm, drm_color_lut_size(crtc_state->hw.degamma_lut) != 1024);
> > +	drm_WARN_ON(&i915->drm, drm_color_lut_size(crtc_state->hw.gamma_lut) != 1024);
> 
> Does it make sense to use some macro for LUT size for split gamma case 
> and regular case?
> 
> Same thing perhaps can be used in ivb_lut_10_size?

I don't think macros would be really helpful. I guess I 
could have used ivb_lut_10_size() for the create_resized_lut()
calls below. And these WARNs I guess could have just used
device info stuff instead. Or I could just drop them entirely
since they aren't really checking anything super important, and
the create_resized_lut() would work with any input LUT size anyway.

Thinking a bit further we could certainly consider extending
the ivb_lut_10_size()/glk_degamma_lut_size() approach to cover
all the gamma modes. Though I think it would probably make sense
to implement that as some kind of struct based approach where we
describe each LUT format in a struct. Would also be more in line
with what we've been thinking for the uapi revamp.

-- 
Ville Syrjälä
Intel