[PATCH 2/5] drm: Set DRM connector link status property

[Manasi Navare]

In the usual working scenarios, this property is "Good".
If something fails during modeset, the DRM driver can
set the link status to "Bad", prune the mode list based on the
link rate/lane count fallback values and send  hotplug uevent
so that userspace that is aware of this property can take an
appropriate action by reprobing connectors and re triggering
a modeset to improve user experience and avoid black screens.
In case of userspace that is not aware of this link status
property, the user experience will be unchanged.

The reason for adding the property is to handle link training failures,
but it is not limited to DP or link training. For example, if we
implement asynchronous setcrtc, we can use this to report any failures
in that.

Cc: dri-devel at lists.freedesktop.org
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Daniel Vetter <daniel.vetter at intel.com>
Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
---
 drivers/gpu/drm/drm_connector.c | 38 ++++++++++++++++++++++++++++++++++++++
 include/drm/drm_connector.h     |  2 ++
 2 files changed, 40 insertions(+)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index d4e852f..09f4093 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -968,6 +968,44 @@ int drm_mode_connector_update_edid_property(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_mode_connector_update_edid_property);
 
+/**
+ * drm_mode_connector_set_link_status_property - Set the link status property of
+ * a connector to indicate status of link as a result of link training.
+ * @connector: drm connector
+ * @link_status: new value of link status property (0: Good, 1: Bad)
+ *
+ * In usual working scenario, this link status property will always be set to
+ * "GOOD".
+ * If something fails during or after a mode set, the kernel driver can set this
+ * link status to "BAD", prune the mode list based on new information and send a
+ * hotplug uevent for userspace to have it re-check the valid modes through
+ * Get_connector and try again.
+ *
+ * If userspace is not aware of this property, the user experience is the same
+ * as it currently is. If the userspace is aware of the property, it has a chance
+ * to improve user experience by handling link training failures, avoiding black
+ * screens. The DRM driver can chose to not modify property and keep link status
+ * as "GOOD" always to keep the user experience same as it currently is.
+ *
+ * The reason for adding this property is to handle link training failures, but
+ * it is not limited to DP or link training. For example, if we implement
+ * asynchronous setcrtc, this property can be used to reportany failures in that.
+ *
+ * This function must be called from asynchronous work item.
+ * Returns zero on success and negative errrno on failure.
+ */
+int drm_mode_connector_set_link_status_property(struct drm_connector *connector,
+						uint64_t link_status)
+{
+	struct drm_device *dev = connector->dev;
+
+	connector->link_status = link_status;
+	return drm_object_property_set_value(&connector->base,
+					     dev->mode_config.link_status_property,
+					     link_status);
+}
+EXPORT_SYMBOL(drm_mode_connector_set_link_status_property);
+
 int drm_mode_connector_set_obj_prop(struct drm_mode_object *obj,
 				    struct drm_property *property,
 				    uint64_t value)
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index ad5c8b0..ac76469 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -778,6 +778,8 @@ int drm_mode_connector_set_path_property(struct drm_connector *connector,
 int drm_mode_connector_set_tile_property(struct drm_connector *connector);
 int drm_mode_connector_update_edid_property(struct drm_connector *connector,
 					    const struct edid *edid);
+int drm_mode_connector_set_link_status_property(struct drm_connector *connector,
+						uint64_t link_status);
 
 /**
  * drm_for_each_connector - iterate over all connectors
-- 
1.9.1