drm/i915: add i2c symlink under hdmi connector

Currently, the i2c adapter is available only under DP connectors.

Add i2c symlink under hdmi connector pointing to i2c adapter in order to
make this behaviour consistent.

The initial motivation was to make igt i2c subtest
patch [1] work on all connectors.

[1]: https://patchwork.freedesktop.org/series/60357/

v2:
- Moved symlink remove to unregister (Ville)
- Clarified commit message (Jani)
- Changed WARN to DRM_ERROR (Jani)
- Minor codestyle changes proposed by Jani

v3: added blank line

Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Oleg Vasilev <oleg.vasilev@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190520150642.3477-1-oleg.vasilev@intel.com

drivers/gpu/drm/i915/intel_hdmi.c

@@ -2704,6 +2704,36 @@ static void chv_hdmi_pre_enable(struct intel_encoder *encoder,
 	chv_phy_release_cl2_override(encoder);
 }
 
+static struct i2c_adapter *
+intel_hdmi_get_i2c_adapter(struct drm_connector *connector)
+{
+	struct drm_i915_private *dev_priv = to_i915(connector->dev);
+	struct intel_hdmi *intel_hdmi = intel_attached_hdmi(connector);
+
+	return intel_gmbus_get_adapter(dev_priv, intel_hdmi->ddc_bus);
+}
+
+static void intel_hdmi_create_i2c_symlink(struct drm_connector *connector)
+{
+	struct i2c_adapter *adapter = intel_hdmi_get_i2c_adapter(connector);
+	struct kobject *i2c_kobj = &adapter->dev.kobj;
+	struct kobject *connector_kobj = &connector->kdev->kobj;
+	int ret;
+
+	ret = sysfs_create_link(connector_kobj, i2c_kobj, i2c_kobj->name);
+	if (ret)
+		DRM_ERROR("Failed to create i2c symlink (%d)\n", ret);
+}
+
+static void intel_hdmi_remove_i2c_symlink(struct drm_connector *connector)
+{
+	struct i2c_adapter *adapter = intel_hdmi_get_i2c_adapter(connector);
+	struct kobject *i2c_kobj = &adapter->dev.kobj;
+	struct kobject *connector_kobj = &connector->kdev->kobj;
+
+	sysfs_remove_link(connector_kobj, i2c_kobj->name);
+}
+
 static int
 intel_hdmi_connector_register(struct drm_connector *connector)
 {
@@ -2715,6 +2745,8 @@ intel_hdmi_connector_register(struct drm_connector *connector)
 
 	i915_debugfs_connector_add(connector);
 
+	intel_hdmi_create_i2c_symlink(connector);
+
 	return ret;
 }
 
@@ -2726,6 +2758,13 @@ static void intel_hdmi_destroy(struct drm_connector *connector)
 	intel_connector_destroy(connector);
 }
 
+static void intel_hdmi_connector_unregister(struct drm_connector *connector)
+{
+	intel_hdmi_remove_i2c_symlink(connector);
+
+	intel_connector_unregister(connector);
+}
+
 static const struct drm_connector_funcs intel_hdmi_connector_funcs = {
 	.detect = intel_hdmi_detect,
 	.force = intel_hdmi_force,
@@ -2733,7 +2772,7 @@ static const struct drm_connector_funcs intel_hdmi_connector_funcs = {
 	.atomic_get_property = intel_digital_connector_atomic_get_property,
 	.atomic_set_property = intel_digital_connector_atomic_set_property,
 	.late_register = intel_hdmi_connector_register,
-	.early_unregister = intel_connector_unregister,
+	.early_unregister = intel_hdmi_connector_unregister,
 	.destroy = intel_hdmi_destroy,
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 	.atomic_duplicate_state = intel_digital_connector_duplicate_state,