[PATCH 09/11] drm/dp_mst: Add drm_dp_mst_aux_for_parent()

[Imre Deak <imre.deak@xxxxxxxxx>]

Add a function to get the AUX device of the parent of an MST port, used
by a follow-up i915 patch in the patchset.

Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
---
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 6bd471a2266ce..d70f7de644371 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -6004,6 +6004,22 @@ static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
 	return false;
 }
 
+/**
+ * drm_dp_mst_aux_for_parent() - Get the AUX device for an MST port's parent
+ * @port: MST port whose parent's AUX device is returned
+ *
+ * Return the AUX device for @port's parent or NULL if port's parent is the
+ * root port.
+ */
+struct drm_dp_aux *drm_dp_mst_aux_for_parent(struct drm_dp_mst_port *port)
+{
+	if (!port->parent || !port->parent->port_parent)
+		return NULL;
+
+	return &port->parent->port_parent->aux;
+}
+EXPORT_SYMBOL(drm_dp_mst_aux_for_parent);
+
 /**
  * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
  * @port: The port to check. A leaf of the MST tree with an attached display.
-- 
2.43.3