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]. v2: - Change wording to avoid "enabled" (Daniel) - Add paragraph about multiple connectors sharing the same CRTC (Pekka) - Add paragraph about performing an atomic commit on a connector without updating the link-status property (Daniel) v3: - Fix description of what happens when link-status isn't reset to "GOOD", and when link-status is reset without ALLOW_MODESET (Daniel, Ville) - Changing link-status to "BAD" is a no-op - Clearly state that "BAD" means black screen (Manasi) [1]: https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/commit/fbe61f529737191d0920521946a575bd55f00fbe Signed-off-by: Simon Ser <contact@xxxxxxxxxxx> Cc: Daniel Vetter <daniel@xxxxxxxx> Cc: Manasi Navare <manasi.d.navare@xxxxxxxxx> Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx> Cc: Pekka Paalanen <ppaalanen@xxxxxxxxx> --- I'm not 100% sure the paragraph about not resetting link-status or not using ALLOW_MODESET is accurate. Just like the previous version, this is just an attempt at documenting the current kernel behaviour. drivers/gpu/drm/drm_connector.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index f2b20fd66319..1df036b3353b 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -994,6 +994,26 @@ 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 sink doesn't receive pixels anymore (e.g. the screen + * becomes completely black). 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. + * + * If multiple connectors share the same CRTC and one of them gets a "BAD" + * link-status, the other are unaffected (ie. the sinks still continue to + * receive pixels). + * + * When user-space performs an atomic commit on a connector with a "BAD" + * link-status without resetting the property to "GOOD", the sink may + * still not receive pixels. When user-space performs an atomic commit + * which resets the link-status property to "GOOD" without the + * ALLOW_MODESET flag set, it might fail because a modeset is required. + * + * User-space can only change link-status to "GOOD", changing it to "BAD" + * is a no-op. * 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 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
