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

[Sam McNally <sammc@chromium.org>]

As of commit d8bd15b37d32 ("drm/dp_mst: Fix the DDC I2C device
registration of an MST port"), DP MST DDC I2C devices are consistently
parented to the underlying DRM device, making it challenging to
associate the ddc i2c device with its connector from userspace.

Given the need for further refactoring before the i2c devices can be
parented to their connectors, 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
during late connector registration.

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

 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 1ac874e4e7a1..73a2299c2faa 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2161,11 +2161,23 @@ 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);
 
@@ -5490,6 +5502,7 @@ 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;
@@ -5504,7 +5517,17 @@ 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;
 }
 
 /**
@@ -5513,6 +5536,8 @@ 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.rc0.142.g3c755180ce-goog