[RFC PATCH v1 03/12] drm/connector: extend PATH property to covert Type-C case

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

Userspace needs to identify whether the DisplayPort connector is a
native one or it is wrapped into the USB-C port. Moreover the userspace
might need to point user to the exact location of this Type-C port on
the laptop case.

Existing USB-C altmode implementations (i915, amdgpu) have used the
DRM_MODE_CONNECTOR_DisplayPort even for such ports. To keep backwards
compatibility we can not change this to DRM_MODE_CONNECTOR_USB.
Therefore the kernel needs some other way to represent this information.

To facilitate this, reuse the 'PATH' property, which was used to
describe the DP port in the DP MST configuration. Use either
'typec:portN' to point out to the Type-C port class device, or just
'typec:' if the corresponding port can not be identified.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
 drivers/gpu/drm/drm_connector.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 05fc29a54801..a326782e936e 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -1185,10 +1185,14 @@ static const u32 dp_colorspaces =
  * 	never read back the value of "DPMS" because it can be incorrect.
  * PATH:
  * 	Connector path property to identify how this sink is physically
- * 	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
+ * 	connected. This should be set by calling
+ * 	drm_connector_set_path_property(). Userspace cannot change this
  * 	property.
+ * 	In the case of DP MST this is equal to the path property the MST
+ * 	manager created. It is equal to 'mst:baseID-port-port...'.
+ * 	In the case of DP USB-C connector this is equal to the 'typec:portN',
+ * 	pointing to the corresponding Type-C port device or just 'typec' if the
+ * 	corresponding Type-C port can not be identified.
  * 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
-- 
2.39.2