RE: [PATCH 02/21] drm: Add Plane Degamma Mode property

["Shankar, Uma" <uma.shankar@intel.com>]

> -----Original Message-----
> From: Harry Wentland <harry.wentland@amd.com>
> Sent: Friday, June 4, 2021 11:54 PM
> To: Shankar, Uma <uma.shankar@intel.com>; intel-gfx@lists.freedesktop.org; dri-
> devel@lists.freedesktop.org
> Cc: Modem, Bhanuprakash <bhanuprakash.modem@intel.com>; Cyr, Aric
> <Aric.Cyr@amd.com>
> Subject: Re: [PATCH 02/21] drm: Add Plane Degamma Mode property
> 
> On 2021-06-01 6:51 a.m., Uma Shankar wrote:
> > Add Plane Degamma Mode as an enum property. Create a helper function
> > for all plane color management features.
> >
> > This is an enum property with values as blob_id's and exposes the
> > various gamma modes supported and the lut ranges. Getting the blob id
> > in userspace, user can get the mode supported and also the range of
> > gamma mode supported with number of lut coefficients. It can then set
> > one of the modes using this enum property.
> >
> > Lut values will be sent through separate GAMMA_LUT blob property.
> >
> > Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> > ---
> >  Documentation/gpu/drm-kms.rst             | 90 ++++++++++++++++++++++
> >  drivers/gpu/drm/drm_atomic.c              |  1 +
> >  drivers/gpu/drm/drm_atomic_state_helper.c |  2 +
> >  drivers/gpu/drm/drm_atomic_uapi.c         |  4 +
> >  drivers/gpu/drm/drm_color_mgmt.c          | 93 ++++++++++++++++++++++-
> >  include/drm/drm_mode_object.h             |  2 +-
> >  include/drm/drm_plane.h                   | 23 ++++++
> >  7 files changed, 212 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/gpu/drm-kms.rst
> > b/Documentation/gpu/drm-kms.rst index 87e5023e3f55..752be545e7d7
> > 100644
> > --- a/Documentation/gpu/drm-kms.rst
> > +++ b/Documentation/gpu/drm-kms.rst
> > @@ -514,9 +514,99 @@ Damage Tracking Properties  Color Management
> > Properties
> >  ---------------------------
> >
> > +Below is how a typical hardware pipeline for color will look like:
> > +
> > +.. kernel-render:: DOT
> > +   :alt: Display Color Pipeline
> > +   :caption: Display Color Pipeline Overview
> > +
> > +   digraph "KMS" {
> > +      node [shape=box]
> > +
> > +      subgraph cluster_static {
> > +          style=dashed
> > +          label="Display Color Hardware Blocks"
> > +
> > +          node [bgcolor=grey style=filled]
> > +          "Plane Degamma A" -> "Plane CSC/CTM A"
> > +          "Plane CSC/CTM A" -> "Plane Gamma A"
> > +          "Pipe Blender" [color=lightblue,style=filled, width=5.25, height=0.75];
> > +          "Plane Gamma A" -> "Pipe Blender"
> > +	  "Pipe Blender" -> "Pipe DeGamma"
> > +          "Pipe DeGamma" -> "Pipe CSC/CTM"
> > +          "Pipe CSC/CTM" -> "Pipe Gamma"
> > +          "Pipe Gamma" -> "Pipe Output"
> > +      }
> > +
> 
> It might be worthwhile to also highlight the YCbCr coefficient matrix in the pipeline,
> between the FB and Plane degamma, i.e.
>   YCbCr coefficients > plane degamma > csc > ...
> 
> One problem with this view is that not all HW will support all (or any) of these CM
> blocks on all planes. For example, on AMD HW cursors are very different from other
> planes and don't really have full CM support.
> 
> > +      subgraph cluster_static {
> > +          style=dashed
> > +
> > +          node [shape=box]
> > +          "Plane Degamma B" -> "Plane CSC/CTM B"
> > +          "Plane CSC/CTM B" -> "Plane Gamma B"
> > +          "Plane Gamma B" -> "Pipe Blender"
> > +      }
> > +
> > +      subgraph cluster_static {
> > +          style=dashed
> > +
> > +          node [shape=box]
> > +          "Plane Degamma C" -> "Plane CSC/CTM C"
> > +          "Plane CSC/CTM C" -> "Plane Gamma C"
> > +          "Plane Gamma C" -> "Pipe Blender"
> > +      }
> > +
> > +      subgraph cluster_fb {
> > +          style=dashed
> > +          label="RAM"
> > +
> > +          node [shape=box width=1.7 height=0.2]
> > +
> > +          "FB 1" -> "Plane Degamma A"
> > +          "FB 2" -> "Plane Degamma B"
> > +          "FB 3" -> "Plane Degamma C"
> > +      }
> > +   }
> > +
> > +In real world usecases,
> > +
> > +1. Plane Degamma can be used to linearize a non linear gamma encoded
> > +framebuffer. This is needed to do any linear math like color space
> > +conversion. For ex, linearize frames encoded in SRGB or by HDR curve.
> > +
> > +2. Later Plane CTM block can convert the content to some different
> > +colorspace. For ex, SRGB to BT2020 etc.
> > +
> > +3. Plane Gamma block can be used later to re-apply the non-linear
> > +curve. This can also be used to apply Tone Mapping for HDR usecases.
> > +
> 
> This would mean you're blending in gamma space which is likely not what most
> compositors expect. There are numerous articles that describe why blending in
> gamma space is problematic, such as [1]
> 
> [1] https://ninedegreesbelow.com/photography/linear-gamma-blur-normal-
> blend.html
> 
> To blend in linear space this should be configured to do
> 
>   Plane Degamma > Plane CTM > CRTC Gamma
> 
> I think it would also be good if we moved away from calling this gamma. It's really
> only gamma for legacy SDR scenarios. For HDR cases I would never expect these to
> use gamma and even though the sRGB transfer function is based on gamma
> functions it's complicated [2].
> 
> [2] https://en.wikipedia.org/wiki/SRGB
> 
> A better way to describe these would be as "transfer function" and "inverse transfer
> function." The space at various stages could then be described as linear or non-
> linear, specifically PQ, HLG, sRGB, BT709, or using another transfer function.

Yeah I just kept the naming based on what we had for crtc to avoid ambiguity. But yes, we
can rename these to have them named generically, as gamma lut actually can be used for
Tone mapping as well and its not just meant for applying a fixed non liner curve only. However
naming based on transfer function is also not optimum as Tone mapping is not related to transfer
function. May be we can name them as:
linear_lut and nl_tone_mapper_lut.

Other ideas for names are welcome.

Regards,
Uma Shankar


> Harry
> 
> > +All the layers or framebuffers need to be converted to same color
> > +space and format before blending. The plane color hardware blocks can
> > +help with this. Once the Data is blended, similar color processing
> > +can be done on blended output using pipe color hardware blocks.
> > +
> > +DRM Properties have been created to define and expose all these
> > +hardware blocks to userspace. A userspace application (compositor or
> > +any color app) can use these interfaces and define policies to
> > +efficiently use the display hardware for such color operations.
> > +
> > +Pipe Color Management Properties
> > +---------------------------------
> > +
> >  .. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
> >     :doc: overview
> >
> > +Plane Color Management Properties
> > +---------------------------------
> > +
> > +.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
> > +   :doc: Plane Color Properties
> > +
> > +.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
> > +   :doc: export
> > +
> >  Tile Group Property
> >  -------------------
> >
> > diff --git a/drivers/gpu/drm/drm_atomic.c
> > b/drivers/gpu/drm/drm_atomic.c index a8bbb021684b..8892d03602f7 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -708,6 +708,7 @@ static void drm_atomic_plane_print_state(struct
> drm_printer *p,
> >  		   drm_get_color_encoding_name(state->color_encoding));
> >  	drm_printf(p, "\tcolor-range=%s\n",
> >  		   drm_get_color_range_name(state->color_range));
> > +	drm_printf(p, "\tcolor_mgmt_changed=%d\n",
> > +state->color_mgmt_changed);
> >
> >  	if (plane->funcs->atomic_print_state)
> >  		plane->funcs->atomic_print_state(p, state); diff --git
> > a/drivers/gpu/drm/drm_atomic_state_helper.c
> > b/drivers/gpu/drm/drm_atomic_state_helper.c
> > index ddcf5c2c8e6a..f26b03853711 100644
> > --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> > @@ -311,6 +311,8 @@ void __drm_atomic_helper_plane_duplicate_state(struct
> drm_plane *plane,
> >  	state->fence = NULL;
> >  	state->commit = NULL;
> >  	state->fb_damage_clips = NULL;
> > +
> > +	state->color_mgmt_changed = false;
> >  }
> >  EXPORT_SYMBOL(__drm_atomic_helper_plane_duplicate_state);
> >
> > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c
> > b/drivers/gpu/drm/drm_atomic_uapi.c
> > index 438e9585b225..40fa05fa33dc 100644
> > --- a/drivers/gpu/drm/drm_atomic_uapi.c
> > +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> > @@ -595,6 +595,8 @@ static int drm_atomic_plane_set_property(struct
> drm_plane *plane,
> >  		state->color_encoding = val;
> >  	} else if (property == plane->color_range_property) {
> >  		state->color_range = val;
> > +	} else if (property == plane->degamma_mode_property) {
> > +		state->degamma_mode = val;
> >  	} else if (property == config->prop_fb_damage_clips) {
> >  		ret = drm_atomic_replace_property_blob_from_id(dev,
> >  					&state->fb_damage_clips,
> > @@ -661,6 +663,8 @@ drm_atomic_plane_get_property(struct drm_plane
> *plane,
> >  		*val = state->color_encoding;
> >  	} else if (property == plane->color_range_property) {
> >  		*val = state->color_range;
> > +	} else if (property == plane->degamma_mode_property) {
> > +		*val = state->degamma_mode;
> >  	} else if (property == config->prop_fb_damage_clips) {
> >  		*val = (state->fb_damage_clips) ?
> >  			state->fb_damage_clips->base.id : 0; diff --git
> > a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> > index bb14f488c8f6..085ed0d0db00 100644
> > --- a/drivers/gpu/drm/drm_color_mgmt.c
> > +++ b/drivers/gpu/drm/drm_color_mgmt.c
> > @@ -34,8 +34,8 @@
> >  /**
> >   * DOC: overview
> >   *
> > - * Color management or color space adjustments is supported through a
> > set of 5
> > - * properties on the &drm_crtc object. They are set up by calling
> > + * Pipe Color management or color space adjustments is supported
> > + through a
> > + * set of 5 properties on the &drm_crtc object. They are set up by
> > + calling
> >   * drm_crtc_enable_color_mgmt().
> >   *
> >   * "DEGAMMA_LUT”:
> > @@ -584,6 +584,95 @@ int drm_plane_create_color_properties(struct
> > drm_plane *plane,  }
> > EXPORT_SYMBOL(drm_plane_create_color_properties);
> >
> > +/**
> > + * DOC: Plane Color Properties
> > + *
> > + * Plane Color management or color space adjustments is supported
> > + * through a set of 5 properties on the &drm_plane object.
> > + *
> > + * degamma_mode_property:
> > + *     Blob property which advertizes the possible degamma modes and
> > + *     lut ranges supported by the platform. This  allows userspace
> > + *     to query and get the plane degamma color caps and choose the
> > + *     appropriate degamma mode and create lut values accordingly
> > + *
> > + */
> > +int drm_plane_create_color_mgmt_properties(struct drm_device *dev,
> > +					   struct drm_plane *plane,
> > +					   int num_values)
> > +{
> > +	struct drm_property *prop;
> > +
> > +	prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
> > +				   "PLANE_DEGAMMA_MODE", num_values);
> > +	if (!prop)
> > +		return -ENOMEM;
> > +
> > +	plane->degamma_mode_property = prop;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_plane_create_color_mgmt_properties);
> > +
> > +void drm_plane_attach_degamma_properties(struct drm_plane *plane) {
> > +	if (!plane->degamma_mode_property)
> > +		return;
> > +
> > +	drm_object_attach_property(&plane->base,
> > +				   plane->degamma_mode_property, 0); }
> > +EXPORT_SYMBOL(drm_plane_attach_degamma_properties);
> > +
> > +int drm_plane_color_add_gamma_degamma_mode_range(struct drm_plane
> *plane,
> > +						 const char *name,
> > +						 const struct drm_color_lut_range
> *ranges,
> > +						 size_t length, enum lut_type type)
> {
> > +	struct drm_property_blob *blob;
> > +	struct drm_property *prop = NULL;
> > +	int num_ranges = length / sizeof(ranges[0]);
> > +	int i, ret, num_types_0;
> > +
> > +	if (type == LUT_TYPE_DEGAMMA)
> > +		prop = plane->degamma_mode_property;
> > +
> > +	if (!prop)
> > +		return -EINVAL;
> > +
> > +	if (length == 0 && name)
> > +		return drm_property_add_enum(prop, 0, name);
> > +
> > +	if (WARN_ON(length == 0 || length % sizeof(ranges[0]) != 0))
> > +		return -EINVAL;
> > +	num_types_0 = hweight8(ranges[0].flags & (DRM_MODE_LUT_GAMMA |
> > +			       DRM_MODE_LUT_DEGAMMA));
> > +	if (num_types_0 == 0)
> > +		return -EINVAL;
> > +
> > +	for (i = 1; i < num_ranges; i++) {
> > +		int num_types = hweight8(ranges[i].flags &
> (DRM_MODE_LUT_GAMMA |
> > +					 DRM_MODE_LUT_DEGAMMA));
> > +
> > +		/* either all ranges have DEGAMMA|GAMMA or none have it */
> > +		if (num_types_0 != num_types)
> > +			return -EINVAL;
> > +	}
> > +
> > +	blob = drm_property_create_blob(plane->dev, length, ranges);
> > +	if (IS_ERR(blob))
> > +		return PTR_ERR(blob);
> > +
> > +	ret = drm_property_add_enum(prop, blob->base.id, name);
> > +	if (ret) {
> > +		drm_property_blob_put(blob);
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_plane_color_add_gamma_degamma_mode_range);
> > +
> >  /**
> >   * drm_color_lut_check - check validity of lookup table
> >   * @lut: property blob containing LUT to check diff --git
> > a/include/drm/drm_mode_object.h b/include/drm/drm_mode_object.h index
> > c34a3e8030e1..d4128c7daa08 100644
> > --- a/include/drm/drm_mode_object.h
> > +++ b/include/drm/drm_mode_object.h
> > @@ -60,7 +60,7 @@ struct drm_mode_object {
> >  	void (*free_cb)(struct kref *kref);
> >  };
> >
> > -#define DRM_OBJECT_MAX_PROPERTY 24
> > +#define DRM_OBJECT_MAX_PROPERTY 26
> >  /**
> >   * struct drm_object_properties - property tracking for &drm_mode_object
> >   */
> > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h index
> > 1294610e84f4..e476a5939f8e 100644
> > --- a/include/drm/drm_plane.h
> > +++ b/include/drm/drm_plane.h
> > @@ -236,6 +236,15 @@ struct drm_plane_state {
> >
> >  	/** @state: backpointer to global drm_atomic_state */
> >  	struct drm_atomic_state *state;
> > +
> > +	/**
> > +	 * @degamma_mode: This is a blob_id and exposes the platform capabilities
> > +	 * wrt to various gamma modes and the respective lut ranges. This also
> > +	 * helps user select a degamma mode amongst the supported ones.
> > +	 */
> > +	u32 degamma_mode;
> > +
> > +	u8 color_mgmt_changed : 1;
> >  };
> >
> >  static inline struct drm_rect
> > @@ -747,6 +756,12 @@ struct drm_plane {
> >  	 * scaling.
> >  	 */
> >  	struct drm_property *scaling_filter_property;
> > +
> > +	/**
> > +	 * @degamma_mode_property: Optional Plane property to set the LUT
> > +	 * used to convert the framebuffer's colors to linear gamma.
> > +	 */
> > +	struct drm_property *degamma_mode_property;
> >  };
> >
> >  #define obj_to_plane(x) container_of(x, struct drm_plane, base) @@
> > -838,6 +853,14 @@ void drm_plane_force_disable(struct drm_plane
> > *plane);  int drm_mode_plane_set_obj_prop(struct drm_plane *plane,
> >  				       struct drm_property *property,
> >  				       uint64_t value);
> > +int drm_plane_create_color_mgmt_properties(struct drm_device *dev,
> > +					   struct drm_plane *plane,
> > +					   int num_values);
> > +void drm_plane_attach_degamma_properties(struct drm_plane *plane);
> > +int drm_plane_color_add_gamma_degamma_mode_range(struct drm_plane
> *plane,
> > +						 const char *name,
> > +						 const struct drm_color_lut_range
> *ranges,
> > +						 size_t length, enum lut_type type);
> >
> >  /**
> >   * drm_plane_find - find a &drm_plane
> >