[PATCH v3 1/2] drm: drm/i915: Add connector property to limit max bpc

[Radhakrishna Sripada <radhakrishna.sripada@intel.com>]

At times 12bpc HDMI cannot be driven due to faulty cables, dongles
level shifters etc. To workaround them we may need to drive the output
at a lower bpc. Currently the user space does not have a way to limit
the bpc. The default bpc to be programmed is decided by the driver and
is run against connector limitations.

Creating a new connector property "max bpc" in order to limit the bpc
with which the pixels are scanned out. xrandr can make use of this
connector property to make sure that bpc does not exceed the configured value.
This property can be used by userspace to set the bpc.

V2: Initialize max_bpc to satisfy kms_properties
V3: Move the property to drm_connector

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Kishore Kadiyala <kishore.kadiyala@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
---
 drivers/gpu/drm/drm_atomic.c        |  4 ++++
 drivers/gpu/drm/drm_atomic_helper.c |  4 ++++
 drivers/gpu/drm/i915/intel_drv.h    |  2 ++
 drivers/gpu/drm/i915/intel_hdmi.c   | 11 +++++++++++
 drivers/gpu/drm/i915/intel_modes.c  | 20 ++++++++++++++++++++
 include/drm/drm_connector.h         |  6 ++++++
 include/drm/drm_mode_config.h       |  5 +++++
 7 files changed, 52 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 3eb061e11e2e..461dde0c2c10 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1416,6 +1416,8 @@ static int drm_atomic_connector_set_property(struct drm_connector *connector,
 
 		return set_out_fence_for_connector(state->state, connector,
 						   fence_ptr);
+	} else if (property == config->max_bpc_property) {
+		state->max_bpc = val;
 	} else if (connector->funcs->atomic_set_property) {
 		return connector->funcs->atomic_set_property(connector,
 				state, property, val);
@@ -1511,6 +1513,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
 		*val = 0;
 	} else if (property == config->writeback_out_fence_ptr_property) {
 		*val = 0;
+	} else if (property == config->max_bpc_property) {
+		*val = state->max_bpc;
 	} else if (connector->funcs->atomic_get_property) {
 		return connector->funcs->atomic_get_property(connector,
 				state, property, val);
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 38ce9a375ffb..82caac8d1432 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -638,6 +638,10 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 			if (old_connector_state->link_status !=
 			    new_connector_state->link_status)
 				new_crtc_state->connectors_changed = true;
+
+			if (old_connector_state->max_bpc !=
+			    new_connector_state->max_bpc)
+				new_crtc_state->connectors_changed = true;
 		}
 
 		if (funcs->atomic_check)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 1b78de838c18..209eb1798238 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1862,6 +1862,8 @@ int intel_ddc_get_modes(struct drm_connector *c, struct i2c_adapter *adapter);
 void intel_attach_force_audio_property(struct drm_connector *connector);
 void intel_attach_broadcast_rgb_property(struct drm_connector *connector);
 void intel_attach_aspect_ratio_property(struct drm_connector *connector);
+void intel_attach_max_bpc_property(struct drm_connector *connector, int min, int
+				   max);
 
 
 /* intel_overlay.c */
diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index a1799b5c12bb..82739f342246 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -2097,11 +2097,22 @@ static const struct drm_encoder_funcs intel_hdmi_enc_funcs = {
 static void
 intel_hdmi_add_properties(struct intel_hdmi *intel_hdmi, struct drm_connector *connector)
 {
+	struct drm_i915_private *dev_priv = to_i915(connector->dev);
+
 	intel_attach_force_audio_property(connector);
 	intel_attach_broadcast_rgb_property(connector);
 	intel_attach_aspect_ratio_property(connector);
 	drm_connector_attach_content_type_property(connector);
 	connector->state->picture_aspect_ratio = HDMI_PICTURE_ASPECT_NONE;
+
+	if (IS_G4X(dev_priv) || IS_VALLEYVIEW(dev_priv) ||
+	    IS_CHERRYVIEW(dev_priv)) {
+		intel_attach_max_bpc_property(connector, 8, 10);
+		connector->state->max_bpc = 10;
+	} else if (INTEL_GEN(dev_priv) >= 5) {
+		intel_attach_max_bpc_property(connector, 8, 12);
+		connector->state->max_bpc = 12;
+	}
 }
 
 /*
diff --git a/drivers/gpu/drm/i915/intel_modes.c b/drivers/gpu/drm/i915/intel_modes.c
index ca44bf368e24..78f2ce92f194 100644
--- a/drivers/gpu/drm/i915/intel_modes.c
+++ b/drivers/gpu/drm/i915/intel_modes.c
@@ -133,3 +133,23 @@ intel_attach_aspect_ratio_property(struct drm_connector *connector)
 			connector->dev->mode_config.aspect_ratio_property,
 			DRM_MODE_PICTURE_ASPECT_NONE);
 }
+
+void
+intel_attach_max_bpc_property(struct drm_connector *connector, int min, int
+			       max)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_mode_config *config = &dev->mode_config;
+	struct drm_property *prop;
+
+	prop = config->max_bpc_property;
+	if (prop == NULL) {
+		prop = drm_property_create_range(dev, 0, "max bpc", min, max);
+		if (prop == NULL)
+			return;
+
+		config->max_bpc_property = prop;
+	}
+
+	drm_object_attach_property(&connector->base, prop, max);
+}
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 97ea41dc678f..d59b9e34ae80 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -460,6 +460,12 @@ struct drm_connector_state {
 	 * drm_writeback_signal_completion()
 	 */
 	struct drm_writeback_job *writeback_job;
+
+	/**
+	 * @max_bpc: Connector property to limit the maximum bit depth of
+	 * the pixels being scanned out.
+	 */
+	unsigned int max_bpc;
 };
 
 /**
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index a0b202e1d69a..b9cd7a73b244 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -562,6 +562,11 @@ struct drm_mode_config {
 	 */
 	struct drm_property *link_status_property;
 	/**
+	 * @max_bpc_property: Default connector property for the max bpc to be
+	 * driven out of the connector.
+	 */
+	struct drm_property *max_bpc_property;
+	/**
 	 * @plane_type_property: Default plane property to differentiate
 	 * CURSOR, PRIMARY and OVERLAY legacy uses of planes.
 	 */
-- 
2.9.3

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