linux-kernel - Re: [PATCH v2 19/34] drm/amd/display: decouple steps for mapping CRTC degamma to DC plane

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Date:   Fri, 25 Aug 2023 13:29:44 -0100
From:   Melissa Wen <mwen@...lia.com>
To:     Pekka Paalanen <pekka.paalanen@...labora.com>
Cc:     amd-gfx@...ts.freedesktop.org,
        Harry Wentland <harry.wentland@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        sunpeng.li@....com, Alex Deucher <alexander.deucher@....com>,
        dri-devel@...ts.freedesktop.org, christian.koenig@....com,
        Xinhui.Pan@....com, airlied@...il.com, daniel@...ll.ch,
        Joshua Ashton <joshua@...ggi.es>,
        Sebastian Wick <sebastian.wick@...hat.com>,
        Xaver Hugl <xaver.hugl@...il.com>,
        Shashank Sharma <Shashank.Sharma@....com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        sungjoon.kim@....com, Alex Hung <alex.hung@....com>,
        Simon Ser <contact@...rsion.fr>, kernel-dev@...lia.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 19/34] drm/amd/display: decouple steps for mapping
 CRTC degamma to DC plane

On 08/22, Pekka Paalanen wrote:
> On Thu, 10 Aug 2023 15:02:59 -0100
> Melissa Wen <mwen@...lia.com> wrote:
> 
> > The next patch adds pre-blending degamma to AMD color mgmt pipeline, but
> > pre-blending degamma caps (DPP) is currently in use to provide DRM CRTC
> > atomic degamma or implict degamma on legacy gamma. Detach degamma usage
> > regarging CRTC color properties to manage plane and CRTC color
> > correction combinations.
> > 
> > Reviewed-by: Harry Wentland <harry.wentland@....com>
> > Signed-off-by: Melissa Wen <mwen@...lia.com>
> > ---
> >  .../amd/display/amdgpu_dm/amdgpu_dm_color.c   | 59 +++++++++++++------
> >  1 file changed, 41 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> > index 68e9f2c62f2e..74eb02655d96 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> > @@ -764,20 +764,9 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
> >  	return 0;
> >  }
> >  
> > -/**
> > - * amdgpu_dm_update_plane_color_mgmt: Maps DRM color management to DC plane.
> > - * @crtc: amdgpu_dm crtc state
> > - * @dc_plane_state: target DC surface
> > - *
> > - * Update the underlying dc_stream_state's input transfer function (ITF) in
> > - * preparation for hardware commit. The transfer function used depends on
> > - * the preparation done on the stream for color management.
> > - *
> > - * Returns:
> > - * 0 on success. -ENOMEM if mem allocation fails.
> > - */
> > -int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
> > -				      struct dc_plane_state *dc_plane_state)
> > +static int
> > +map_crtc_degamma_to_dc_plane(struct dm_crtc_state *crtc,
> > +			     struct dc_plane_state *dc_plane_state)
> >  {
> >  	const struct drm_color_lut *degamma_lut;
> >  	enum dc_transfer_func_predefined tf = TRANSFER_FUNCTION_SRGB;
> > @@ -800,8 +789,7 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
> >  						 &degamma_size);
> >  		ASSERT(degamma_size == MAX_COLOR_LUT_ENTRIES);
> >  
> > -		dc_plane_state->in_transfer_func->type =
> > -			TF_TYPE_DISTRIBUTED_POINTS;
> > +		dc_plane_state->in_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
> >  
> >  		/*
> >  		 * This case isn't fully correct, but also fairly
> > @@ -837,7 +825,7 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
> >  				   degamma_lut, degamma_size);
> >  		if (r)
> >  			return r;
> > -	} else if (crtc->cm_is_degamma_srgb) {
> > +	} else {
> >  		/*
> >  		 * For legacy gamma support we need the regamma input
> >  		 * in linear space. Assume that the input is sRGB.
> > @@ -847,8 +835,43 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
> >  
> >  		if (tf != TRANSFER_FUNCTION_SRGB &&
> >  		    !mod_color_calculate_degamma_params(NULL,
> > -			    dc_plane_state->in_transfer_func, NULL, false))
> > +							dc_plane_state->in_transfer_func,
> > +							NULL, false))
> >  			return -ENOMEM;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * amdgpu_dm_update_plane_color_mgmt: Maps DRM color management to DC plane.
> > + * @crtc: amdgpu_dm crtc state
> > + * @dc_plane_state: target DC surface
> > + *
> > + * Update the underlying dc_stream_state's input transfer function (ITF) in
> > + * preparation for hardware commit. The transfer function used depends on
> > + * the preparation done on the stream for color management.
> > + *
> > + * Returns:
> > + * 0 on success. -ENOMEM if mem allocation fails.
> > + */
> > +int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
> > +				      struct dc_plane_state *dc_plane_state)
> > +{
> > +	bool has_crtc_cm_degamma;
> > +	int ret;
> > +
> > +	has_crtc_cm_degamma = (crtc->cm_has_degamma || crtc->cm_is_degamma_srgb);
> > +	if (has_crtc_cm_degamma){
> > +		/* AMD HW doesn't have post-blending degamma caps. When DRM
> > +		 * CRTC atomic degamma is set, we maps it to DPP degamma block
> > +		 * (pre-blending) or, on legacy gamma, we use DPP degamma to
> > +		 * linearize (implicit degamma) from sRGB/BT709 according to
> > +		 * the input space.
> 
> Uhh, you can't just move degamma before blending if KMS userspace
> wants it after blending. That would be incorrect behaviour. If you
> can't implement it correctly, reject it.
> 
> I hope that magical unexpected linearization is not done with atomic,
> either.
> 
> Or maybe this is all a lost cause, and only the new color-op pipeline
> UAPI will actually work across drivers.

I agree that crtc degamma is an optional property and should be not
exposed if not available.  I did something in this line for DCE that has
no degamma block[1].  Then, AMD DDX driver stopped to advertise atomic
API for DCE, that was not correct too[2].

But I see it as a lost cause that will only be fixed in a new generic
color API. I don't think we should change it using the current DRM CRTC
API with driver-specific props.

[1] https://lore.kernel.org/amd-gfx/20221103184500.14450-1-mwen@igalia.com/
[2] https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues/67
> 
> 
> Thanks,
> pq
> 
> > +		 */
> > +		ret = map_crtc_degamma_to_dc_plane(crtc, dc_plane_state);
> > +		if (ret)
> > +			return ret;
> >  	} else {
> >  		/* ...Otherwise we can just bypass the DGM block. */
> >  		dc_plane_state->in_transfer_func->type = TF_TYPE_BYPASS;
> 

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