[PATCH] drm: document how user-space should use link-status

[Simon Ser]

Describe what a "BAD" link-status means for user-space and how it should
handle it. The logic described has been implemented in igt [1].

[1]: https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/commit/fbe61f529737191d0920521946a575bd55f00fbe

Signed-off-by: Simon Ser <contact at emersion.fr>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Manasi Navare <manasi.d.navare at intel.com>
Cc: Pekka Paalanen <ppaalanen at gmail.com>
---
 drivers/gpu/drm/drm_connector.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index f2b20fd66319..08ba84f9787a 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -994,6 +994,12 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
  *      after modeset, the kernel driver may set this to "BAD" and issue a
  *      hotplug uevent. Drivers should update this value using
  *      drm_connector_set_link_status_property().
+ *
+ *      When user-space receives the hotplug uevent and detects a "BAD"
+ *      link-status, the connector is no longer enabled. The list of available
+ *      modes may have changed. User-space is expected to pick a new mode if
+ *      the current one has disappeared and perform a new modeset with
+ *      link-status set to "GOOD" to re-enable the connector.
  * non_desktop:
  * 	Indicates the output should be ignored for purposes of displaying a
  * 	standard desktop environment or console. This is most likely because
-- 
2.26.2