[PATCH] drm/connector: hdmi: Add a link bpc property

[Marius Vlad]

From: Derek Foreman <derek.foreman at collabora.com>

Add a way to know the actual bpc of a running link.

Drivers might change the current bpc link value due to changes in mode
line or refresh rates. For example when enabling VRR the underlying
hardware might not be able sustain the same bandwidth for a particular
mode line, and it might attempt to lower the bpc. Another example can be
found when switching the color output format, part of YUV420 fallback.

This means we might be displaying a stale bpc value although it was
modified for different reasons -- like a refresh rate or an output
color format.

This patch introduces a new property 'link bpc' that user-space can
use to get the current bpc value of a running link. In the same
time this would allow user-space set up bpc using 'max_bpc' property.

Signed-off-by: Derek Foreman <derek.foreman at collabora.com>
Signed-off-by: Marius Vlad <marius.vlad at collabora.com>
---
 drivers/gpu/drm/drm_atomic_uapi.c |  5 +++++
 drivers/gpu/drm/drm_connector.c   | 26 ++++++++++++++++++++++++++
 include/drm/drm_connector.h       |  8 ++++++++
 3 files changed, 39 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index ecc73d52bfae..3a2ffb957ade 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -776,6 +776,9 @@ 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->link_bpc_property) {
+		drm_dbg_kms(dev, "only drivers can set link bpc property. Use max_bpc instead\n");
+		return -EINVAL;
 	} else if (property == connector->privacy_screen_sw_state_property) {
 		state->privacy_screen_sw_state = val;
 	} else if (property == connector->broadcast_rgb_property) {
@@ -861,6 +864,8 @@ 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->link_bpc_property) {
+		*val = state->hdmi.output_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 272d6254ea47..7ed27aec0ccc 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -542,6 +542,28 @@ int drmm_connector_init(struct drm_device *dev,
 }
 EXPORT_SYMBOL(drmm_connector_init);
 
+static int
+drm_connector_attach_link_bpc_property(struct drm_connector *connector,
+				       int min, int max)
+{
+	struct drm_device *dev = connector->dev;
+	struct drm_property *prop;
+
+	prop = connector->link_bpc_property;
+	if (prop)
+		return 0;
+
+	prop = drm_property_create_range(dev, 0, "link bpc", min, max);
+	if (!prop)
+		return -ENOMEM;
+
+	connector->link_bpc_property = prop;
+
+	drm_object_attach_property(&connector->base, prop, max);
+
+	return 0;
+}
+
 /**
  * drmm_connector_hdmi_init - Init a preallocated HDMI connector
  * @dev: DRM device
@@ -618,6 +640,10 @@ int drmm_connector_hdmi_init(struct drm_device *dev,
 	drm_connector_attach_max_bpc_property(connector, 8, max_bpc);
 	connector->max_bpc = max_bpc;
 
+	ret = drm_connector_attach_link_bpc_property(connector, 8, max_bpc);
+	if (ret)
+		return ret;
+
 	if (max_bpc > 8)
 		drm_connector_attach_hdr_output_metadata_property(connector);
 
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 8f34f4b8183d..4a50198aa7c0 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -2079,6 +2079,14 @@ struct drm_connector {
 	 */
 	struct drm_property *max_bpc_property;
 
+	/**
+	 * @link_bpc_property: Current connector link bpc set by the driver
+	 *
+	 * This property can be used to retrieve the current link bpc from
+	 * connector_state::hdmi:output_bpc
+	 */
+	struct drm_property *link_bpc_property;
+
 	/** @privacy_screen: drm_privacy_screen for this connector, or NULL. */
 	struct drm_privacy_screen *privacy_screen;
 
-- 
2.47.2