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SubjectRe: [PATCH v4 09/17] drm/uAPI: Add "active color range" drm property as feedback for userspace
On Fri, 18 Jun 2021 11:11:08 +0200
Werner Sembach <wse@tuxedocomputers.com> wrote:

> Add a new general drm property "active color range" which can be used by
> graphic drivers to report the used color range back to userspace.
>
> There was no way to check which color range got actually used on a given
> monitor. To surely predict this, one must know the exact capabilities of
> the monitor and what the default behaviour of the used driver is. This
> property helps eliminating the guessing at this point.
>
> In the future, automatic color calibration for screens might also depend on
> this information being available.
>
> Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
> ---
> drivers/gpu/drm/drm_connector.c | 59 +++++++++++++++++++++++++++++++++
> include/drm/drm_connector.h | 27 +++++++++++++++
> 2 files changed, 86 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index 684d7abdf0eb..818de58d972f 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -897,6 +897,12 @@ static const struct drm_prop_enum_list drm_active_color_format_enum_list[] = {
> { DRM_COLOR_FORMAT_YCRCB420, "ycbcr420" },
> };
>
> +static const struct drm_prop_enum_list drm_active_color_range_enum_list[] = {
> + { DRM_MODE_COLOR_RANGE_UNSET, "Unknown" },
> + { DRM_MODE_COLOR_RANGE_FULL, "Full" },
> + { DRM_MODE_COLOR_RANGE_LIMITED_16_235, "Limited 16:235" },

Doesn't "limited" mean different numbers on RGB vs. Y vs. CbCr? I have
a vague recollection that at least one of them was different from the
others.

Documenting DRM_MODE_COLOR_RANGE_UNSET as "unspecified/default" while
the string for it is "Unknown" seems inconsistent to me. I would
recommend to avoid the word "default" because "reset to defaults" might
become a thing one day, and that probably is not the same default as
here.

Is there actually a case for "unknown"? How can it be not known? Or
does it mean "not applicable"?

Otherwise looks good to me.


Thanks,
pq


> +};
> +
> DRM_ENUM_NAME_FN(drm_get_dp_subconnector_name,
> drm_dp_subconnector_enum_list)
>
> @@ -1221,6 +1227,14 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
> * drm_connector_attach_active_color_format_property() to install this
> * property.
> *
> + * active color range:
> + * This read-only property tells userspace the color range actually used by
> + * the hardware display engine on "the cable" on a connector. The chosen
> + * value depends on hardware capabilities of the monitor and the used color
> + * format. Drivers shall use
> + * drm_connector_attach_active_color_range_property() to install this
> + * property.
> + *
> * Connectors also have one standardized atomic property:
> *
> * CRTC_ID:
> @@ -2264,6 +2278,51 @@ void drm_connector_set_active_color_format_property(struct drm_connector *connec
> }
> EXPORT_SYMBOL(drm_connector_set_active_color_format_property);
>
> +/**
> + * drm_connector_attach_active_color_range_property - attach "active color range" property
> + * @connector: connector to attach active color range property on.
> + *
> + * This is used to check the applied color range on a connector.
> + *
> + * Returns:
> + * Zero on success, negative errno on failure.
> + */
> +int drm_connector_attach_active_color_range_property(struct drm_connector *connector)
> +{
> + struct drm_device *dev = connector->dev;
> + struct drm_property *prop;
> +
> + if (!connector->active_color_range_property) {
> + prop = drm_property_create_enum(dev, DRM_MODE_PROP_IMMUTABLE, "active color range",
> + drm_active_color_range_enum_list,
> + ARRAY_SIZE(drm_active_color_range_enum_list));
> + if (!prop)
> + return -ENOMEM;
> +
> + connector->active_color_range_property = prop;
> + drm_object_attach_property(&connector->base, prop, DRM_MODE_COLOR_RANGE_UNSET);
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(drm_connector_attach_active_color_range_property);
> +
> +/**
> + * drm_connector_set_active_color_range_property - sets the active color range property for a
> + * connector
> + * @connector: drm connector
> + * @active_color_range: color range for the connector currently active on "the cable"
> + *
> + * Should be used by atomic drivers to update the active color range over a connector.
> + */
> +void drm_connector_set_active_color_range_property(struct drm_connector *connector,
> + enum drm_mode_color_range active_color_range)
> +{
> + drm_object_property_set_value(&connector->base, connector->active_color_range_property,
> + active_color_range);
> +}
> +EXPORT_SYMBOL(drm_connector_set_active_color_range_property);
> +
> /**
> * drm_connector_attach_hdr_output_metadata_property - attach "HDR_OUTPUT_METADA" property
> * @connector: connector to attach the property on.
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index 8a5197f14e87..9fb7119b7a02 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -648,6 +648,24 @@ struct drm_tv_connector_state {
> unsigned int hue;
> };
>
> +/**
> + * enum drm_mode_color_range - color_range info for &drm_connector
> + *
> + * This enum is used to represent full or limited color range on the display
> + * connector signal.
> + *
> + * @DRM_MODE_COLOR_RANGE_UNSET: Color range is unspecified/default.
> + * @DRM_MODE_COLOR_RANGE_FULL: Color range is full range, 0-255 for
> + * 8-Bit color depth.
> + * DRM_MODE_COLOR_RANGE_LIMITED_16_235: Color range is limited range, 16-235 for
> + * 8-Bit color depth.
> + */
> +enum drm_mode_color_range {
> + DRM_MODE_COLOR_RANGE_UNSET,
> + DRM_MODE_COLOR_RANGE_FULL,
> + DRM_MODE_COLOR_RANGE_LIMITED_16_235,
> +};
> +
> /**
> * struct drm_connector_state - mutable connector state
> */
> @@ -1392,6 +1410,12 @@ struct drm_connector {
> */
> struct drm_property *active_color_format_property;
>
> + /**
> + * @active_color_range_property: Default connector property for the
> + * active color range to be driven out of the connector.
> + */
> + struct drm_property *active_color_range_property;
> +
> #define DRM_CONNECTOR_POLL_HPD (1 << 0)
> #define DRM_CONNECTOR_POLL_CONNECT (1 << 1)
> #define DRM_CONNECTOR_POLL_DISCONNECT (1 << 2)
> @@ -1719,6 +1743,9 @@ void drm_connector_set_active_bpc_property(struct drm_connector *connector, int
> int drm_connector_attach_active_color_format_property(struct drm_connector *connector);
> void drm_connector_set_active_color_format_property(struct drm_connector *connector,
> u32 active_color_format);
> +int drm_connector_attach_active_color_range_property(struct drm_connector *connector);
> +void drm_connector_set_active_color_range_property(struct drm_connector *connector,
> + enum drm_mode_color_range active_color_range);
>
> /**
> * struct drm_tile_group - Tile group metadata

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