[PATCH v4 1/2] drm: Add connector property to limit max bpc

[Radhakrishna Sripada]

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.
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
V4: Split drm and i915 components(Ville)

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Kishore Kadiyala <kishore.kadiyala at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Manasi Navare <manasi.d.navare at intel.com>
Cc: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
---
 drivers/gpu/drm/drm_atomic.c        | 4 ++++
 drivers/gpu/drm/drm_atomic_helper.c | 4 ++++
 include/drm/drm_connector.h         | 6 ++++++
 include/drm/drm_mode_config.h       | 5 +++++
 4 files changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index d0478abc01bd..4e352fc1f0a0 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1420,6 +1420,8 @@ 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);
@@ -1515,6 +1517,8 @@ 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 2c23a48482da..7f763650a623 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/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 97ea41dc678f..fc11f40aae51 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.
+	 */
+	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