[PATCH v2 1/2] drm/i915: Add connector property to limit max bpc

[Radhakrishna Sripada]

From: "Sripada, Radhakrishna" <radhakrishna.sripada at 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.

Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
Cc: Manasi Navare <manasi.d.navare at intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h     |  1 +
 drivers/gpu/drm/i915/intel_atomic.c |  7 +++++++
 drivers/gpu/drm/i915/intel_drv.h    |  2 ++
 drivers/gpu/drm/i915/intel_hdmi.c   |  1 +
 drivers/gpu/drm/i915/intel_modes.c  | 19 +++++++++++++++++++
 5 files changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 54b5d4c582b6..f74f953d2a7b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2465,6 +2465,7 @@ struct drm_i915_private {
 
 	struct drm_property *broadcast_rgb_property;
 	struct drm_property *force_audio_property;
+	struct drm_property *max_bpc_property;
 
 	/* hda/i915 audio component */
 	struct i915_audio_component *audio_component;
diff --git a/drivers/gpu/drm/i915/intel_atomic.c b/drivers/gpu/drm/i915/intel_atomic.c
index 36d4e635e4ce..d6d836ea1a7f 100644
--- a/drivers/gpu/drm/i915/intel_atomic.c
+++ b/drivers/gpu/drm/i915/intel_atomic.c
@@ -58,6 +58,8 @@ int intel_digital_connector_atomic_get_property(struct drm_connector *connector,
 		*val = intel_conn_state->force_audio;
 	else if (property == dev_priv->broadcast_rgb_property)
 		*val = intel_conn_state->broadcast_rgb;
+	else if (property == dev_priv->max_bpc_property)
+		*val = intel_conn_state->max_bpc;
 	else {
 		DRM_DEBUG_ATOMIC("Unknown property %s\n", property->name);
 		return -EINVAL;
@@ -95,6 +97,11 @@ int intel_digital_connector_atomic_set_property(struct drm_connector *connector,
 		return 0;
 	}
 
+	if (property == dev_priv->max_bpc_property) {
+		intel_conn_state->max_bpc = val;
+		return 0;
+	}
+
 	DRM_DEBUG_ATOMIC("Unknown property %s\n", property->name);
 	return -EINVAL;
 }
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 47d022d48718..27f497d165d6 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -337,6 +337,7 @@ struct intel_digital_connector_state {
 
 	enum hdmi_force_audio force_audio;
 	int broadcast_rgb;
+	int max_bpc;
 };
 
 #define to_intel_digital_connector_state(x) container_of(x, struct intel_digital_connector_state, base)
@@ -1692,6 +1693,7 @@ 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 5132dc814788..64d8e0e5e200 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -1798,6 +1798,7 @@ intel_hdmi_add_properties(struct intel_hdmi *intel_hdmi, struct drm_connector *c
 	intel_attach_force_audio_property(connector);
 	intel_attach_broadcast_rgb_property(connector);
 	intel_attach_aspect_ratio_property(connector);
+	intel_attach_max_bpc_property(connector, 8, 12);
 	connector->state->picture_aspect_ratio = HDMI_PICTURE_ASPECT_NONE;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_modes.c b/drivers/gpu/drm/i915/intel_modes.c
index 28a778b785ac..19a093c0a17e 100644
--- a/drivers/gpu/drm/i915/intel_modes.c
+++ b/drivers/gpu/drm/i915/intel_modes.c
@@ -151,3 +151,22 @@ 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_i915_private *dev_priv = to_i915(dev);
+	struct drm_property *prop;
+
+	prop = dev_priv->max_bpc_property;
+	if (prop == NULL) {
+		prop = drm_property_create_range(dev, 0, "max bpc", min, max);
+		if (prop == NULL)
+			return;
+
+		dev_priv->max_bpc_property = prop;
+	}
+
+	drm_object_attach_property(&connector->base, prop, max);
+}
-- 
2.9.3