Add a new KMS connector property called "min bpc". Its purpose is to allow userspace to mandate that the output bit depth ends up greater than or equal to a specified depth, or else have the commit fail. This is useful for checking for output depth degradation in combination with atomic test commits.
Signed-off-by: Nicolas Frattaroli <[email protected]> --- drivers/gpu/drm/drm_atomic_helper.c | 4 ++ drivers/gpu/drm/drm_atomic_uapi.c | 4 ++ drivers/gpu/drm/drm_connector.c | 77 +++++++++++++++++++++++++++++++++++++ include/drm/drm_connector.h | 13 +++++++ 4 files changed, 98 insertions(+) diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 285aac3554df..613a674ace87 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -739,6 +739,10 @@ drm_atomic_helper_check_modeset(struct drm_device *dev, new_connector_state->max_requested_bpc) new_crtc_state->connectors_changed = true; + if (old_connector_state->min_requested_bpc != + new_connector_state->min_requested_bpc) + new_crtc_state->connectors_changed = true; + if (old_connector_state->color_format != new_connector_state->color_format) new_crtc_state->connectors_changed = true; diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c index 1050dddadb17..0440cb63f786 100644 --- a/drivers/gpu/drm/drm_atomic_uapi.c +++ b/drivers/gpu/drm/drm_atomic_uapi.c @@ -956,6 +956,8 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector, fence_ptr); } else if (property == connector->max_bpc_property) { state->max_requested_bpc = val; + } else if (property == connector->min_bpc_property) { + state->min_requested_bpc = val; } else if (property == connector->privacy_screen_sw_state_property) { state->privacy_screen_sw_state = val; } else if (property == connector->broadcast_rgb_property) { @@ -1043,6 +1045,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector, *val = 0; } else if (property == connector->max_bpc_property) { *val = state->max_requested_bpc; + } else if (property == connector->min_bpc_property) { + *val = state->min_requested_bpc; } else if (property == connector->privacy_screen_sw_state_property) { *val = state->privacy_screen_sw_state; } else if (property == connector->broadcast_rgb_property) { diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index cbb067d02cb9..dcf53cc113b0 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -1738,6 +1738,46 @@ EXPORT_SYMBOL(drm_hdmi_connector_get_output_format_name); * drm_connector_attach_max_bpc_property() to create and attach the * property to the connector during initialization. * + * min bpc: + * This range property is used by userspace to set a minimum bit depth that + * the driver must reach on the connector for a given atomic state. If it + * cannot do so, the atomic commit fails. + * + * The precise definition of minimum bit depth used for the "min bpc" + * property must align with the definition a given driver uses for the + * "max bpc" property, such that when "min bpc" and "max bpc" are set to + * the same value, the allowable range of bit depths is a single set point. + * + * Drivers should ideally use a definition of bit depth that refers to a + * perceptual optical bit depth, meaning it is equivalent to an + * uncompressed optical bit depth for a variety of content to the median + * human eyeball in a variety of viewing environments. The display link's + * actual optical bit depth to represent the data on the wire may be lower + * due to compression techniques, or even higher due to padding. In + * concrete terms, userspace should not need to know how to implement DSC + * compression in order to set a minimum bit depth to the appropriate + * value, and should not need to perform display-protocol-specific + * calculations to set the right on-the-wire format. + * + * Userspace may use the "min bpc" property in combination with performing + * atomic test commits in order to enumerate the possible output bit depths + * for a given configuration. This way, userspace compositors can make + * use-case and content-specific tradeoffs to reach a desired output bit + * depth, such as by using chroma subsampling, or by choosing a lower + * refresh rate mode. + * + * Userspace may use the "min bpc" property in combination with the + * "max bpc" property to know what output bit depth a successful atomic + * commit is using. By setting "min bpc" and "max bpc" to the same value, + * a successful commit will be using an output bit depth of said value. + * + * When "min bpc" is set to a non-zero value, any bit depth degradation + * logic below "min bpc" must be implemented by userspace (through lowering + * "min bpc"), rather than by kernel drivers. For a driver to degrade to an + * uncompressed optical output bit depth below "min bpc" is always a bug no + * matter how good the intentions are, since it renders the property + * useless as an oracle. + * * Connectors also have one standardized atomic property: * * CRTC_ID: @@ -2892,6 +2932,43 @@ int drm_connector_attach_max_bpc_property(struct drm_connector *connector, } EXPORT_SYMBOL(drm_connector_attach_max_bpc_property); +/** + * drm_connector_attach_min_bpc_property - attach "min bpc" property + * @connector: connector to attach min bpc property on. + * @max: The maximum bit depth supported by the connector. + * + * Create and attach the "min bpc" connector property, which is used by + * userspace to require that a certain minimum bit depth is reached by the + * connector on atomic commit. + * + * Returns: + * Zero on success, negative errno on failure. + */ +int drm_connector_attach_min_bpc_property(struct drm_connector *connector, + unsigned int max) +{ + struct drm_device *dev = connector->dev; + struct drm_property *prop; + + if (max > U8_MAX) + return -ERANGE; + + prop = connector->min_bpc_property; + if (!prop) { + prop = drm_property_create_range(dev, 0, "min bpc", 0, max); + if (!prop) + return -ENOMEM; + + connector->min_bpc_property = prop; + } + + drm_object_attach_property(&connector->base, prop, 0); + connector->state->min_requested_bpc = 0; + + return 0; +} +EXPORT_SYMBOL(drm_connector_attach_min_bpc_property); + /** * drm_connector_attach_hdr_output_metadata_property - attach "HDR_OUTPUT_METADATA" property * @connector: connector to attach the property on. diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h index 4317166562cf..63d6ac85b3ec 100644 --- a/include/drm/drm_connector.h +++ b/include/drm/drm_connector.h @@ -1261,6 +1261,11 @@ struct drm_connector_state { */ u8 max_requested_bpc; + /** + * @min_requested_bpc: Minimum output bit depth requested by userspace + */ + u8 min_requested_bpc; + /** * @max_bpc: Connector max_bpc based on the requested max_bpc property * and the connector bpc limitations obtained from edid. @@ -2291,6 +2296,12 @@ struct drm_connector { */ struct drm_property *max_bpc_property; + /** + * @min_bpc_property: Default connector property for the minimum bit + * depth for the output to reach, or the commit to fail otherwise. + */ + struct drm_property *min_bpc_property; + /** @privacy_screen: drm_privacy_screen for this connector, or NULL. */ struct drm_privacy_screen *privacy_screen; @@ -2697,6 +2708,8 @@ int drm_connector_set_orientation_from_panel( struct drm_panel *panel); int drm_connector_attach_max_bpc_property(struct drm_connector *connector, int min, int max); +int drm_connector_attach_min_bpc_property(struct drm_connector *connector, + unsigned int max); void drm_connector_create_privacy_screen_properties(struct drm_connector *conn); void drm_connector_attach_privacy_screen_properties(struct drm_connector *conn); void drm_connector_attach_privacy_screen_provider( -- 2.54.0
