[PATCH v2] drm/dp_mst: Add ddc i2c device links for DP MST connectors

[Sam McNally]

DP MST DDC I2C devices are not parented to their connectors. This makes
it challenging to associate the ddc i2c device with its connector from
userspace. With further refactoring, this can be changed, but in the
meantime, follow the pattern of commit e1a29c6c5955 ("drm: Add ddc link
in sysfs created by drm_connector"), creating sysfs ddc links to the
associated i2c device for MST DP connectors.

If the connector is created and registered before the i2c device, create
the link when registering the i2c device; otherwise, create the link
after registering the connector.

Signed-off-by: Sam McNally <sammc at chromium.org>
---

Changes in v2:
- Reworded description to avoid accusing an innocent commit of
  responsibility for the problem being addressed

 drivers/gpu/drm/drm_dp_mst_topology.c | 29 +++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 17dbed0a9800..e60a6b8af3c1 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2159,11 +2159,23 @@ static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb,
 int drm_dp_mst_connector_late_register(struct drm_connector *connector,
 				       struct drm_dp_mst_port *port)
 {
+	int ret;
 	DRM_DEBUG_KMS("registering %s remote bus for %s\n",
 		      port->aux.name, connector->kdev->kobj.name);
 
 	port->aux.dev = connector->kdev;
-	return drm_dp_aux_register_devnode(&port->aux);
+	ret = drm_dp_aux_register_devnode(&port->aux);
+	if (ret)
+		return ret;
+
+	if (port->pdt != DP_PEER_DEVICE_NONE &&
+	    drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
+		ret = sysfs_create_link(&port->connector->kdev->kobj,
+					&port->aux.ddc.dev.kobj, "ddc");
+		if (ret)
+			drm_dp_aux_unregister_devnode(&port->aux);
+	}
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_mst_connector_late_register);
 
@@ -5439,6 +5451,7 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
 {
 	struct drm_dp_aux *aux = &port->aux;
 	struct device *parent_dev = port->mgr->dev->dev;
+	int ret;
 
 	aux->ddc.algo = &drm_dp_mst_i2c_algo;
 	aux->ddc.algo_data = aux;
@@ -5453,7 +5466,17 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
 	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(parent_dev),
 		sizeof(aux->ddc.name));
 
-	return i2c_add_adapter(&aux->ddc);
+	ret = i2c_add_adapter(&aux->ddc);
+	if (ret)
+		return ret;
+
+	if (port->connector && port->connector->kdev) {
+		ret = sysfs_create_link(&port->connector->kdev->kobj,
+					&port->aux.ddc.dev.kobj, "ddc");
+		if (ret)
+			i2c_del_adapter(&port->aux.ddc);
+	}
+	return ret;
 }
 
 /**
@@ -5462,6 +5485,8 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
  */
 static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port)
 {
+	if (port->connector && port->connector->kdev)
+		sysfs_remove_link(&port->connector->kdev->kobj, "ddc");
 	i2c_del_adapter(&port->aux.ddc);
 }
 
-- 
2.28.0.526.ge36021eeef-goog