[RFC][PATCH 1/2] drm: Improve PATH prop docs

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

The PATH blob is already being parsed by userspace for MST connectors
so the layout of the blob is now uabi. Let's document what it should
look like.

Also add a clear note saying non-MST connectors can have a PATH prop
too.

Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Pekka Paalanen <ppaalanen at gmail.com>
Cc: Ilia Mirkin <imirkin at alum.mit.edu>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/drm_connector.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index e17586aaa80f..ce3926e9ad11 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -899,7 +899,16 @@ static const struct drm_prop_enum_list hdmi_colorspaces[] = {
  * 	connected. Used by DP MST. This should be set by calling
  * 	drm_connector_set_path_property(), in the case of DP MST with the
  * 	path property the MST manager created. Userspace cannot change this
- * 	property.
+ * 	property. The value must be an ASCII string.
+ *
+ * 	For DP MST connectors the path string follows the pattern
+ * 	"mst:<base connector ID>[-<mst port>]...", where the base connector ID
+ * 	identifies the DP connector on the source device, and the mst ports
+ * 	are the port numbers in the DP MST topology.
+ *
+ * 	For non-DP MST connectors the format is freeform, as long as it
+ * 	uniquely identifies the physical path, remains stable across
+ * 	kernel releases, and does not start with "mst:".
  * TILE:
  * 	Connector tile group property to indicate how a set of DRM connector
  * 	compose together into one logical screen. This is used by both high-res
@@ -1678,7 +1687,7 @@ int drm_mode_create_suggested_offset_properties(struct drm_device *dev)
 EXPORT_SYMBOL(drm_mode_create_suggested_offset_properties);
 
 /**
- * drm_connector_set_path_property - set tile property on connector
+ * drm_connector_set_path_property - set path property on connector
  * @connector: connector to set property on.
  * @path: path to use for property; must not be NULL.
  *
-- 
2.21.0