• Lyude Paul's avatar
    drm/dp_mst: Add basic topology reprobing when resuming · 6f85f738
    Lyude Paul authored
    Finally! For a very long time, our MST helpers have had one very
    annoying issue: They don't know how to reprobe the topology state when
    coming out of suspend. This means that if a user has a machine connected
    to an MST topology and decides to suspend their machine, we lose all
    topology changes that happened during that period. That can be a big
    problem if the machine was connected to a different topology on the same
    port before resuming, as we won't bother reprobing any of the ports and
    likely cause the user's monitors not to come back up as expected.
    
    So, we start fixing this by teaching our MST helpers how to reprobe the
    link addresses of each connected topology when resuming. As it turns
    out, the behavior that we want here is identical to the behavior we want
    when initially probing a newly connected MST topology, with a couple of
    important differences:
    
    - We need to be more careful about handling the potential races between
      events from the MST hub that could change the topology state as we're
      performing the link address reprobe
    - We need to be more careful about handling unlikely state changes on
      ports - such as an input port turning into an output port, something
      that would be far more likely to happen in situations like the MST hub
      we're connected to being changed while we're suspend
    
    Both of which have been solved by previous commits. That leaves one
    requirement:
    
    - We need to prune any MST ports in our in-memory topology state that
      were present when suspending, but have not appeared in the post-resume
      link address response from their parent branch device
    
    Which we can now handle in this commit by modifying
    drm_dp_send_link_address(). We then introduce suspend/resume reprobing
    by introducing drm_dp_mst_topology_mgr_invalidate_mstb(), which we call
    in drm_dp_mst_topology_mgr_suspend() to traverse the in-memory topology
    state to indicate that each mstb needs it's link address resent and PBN
    resources reprobed.
    
    On resume, we start back up &mgr->work and have it reprobe the topology
    in the same way we would on a hotplug, removing any leftover ports that
    no longer appear in the topology state.
    
    Changes since v4:
    * Split indenting changes in drm_dp_mst_topology_mgr_resume() into a
      separate patch
    * Only fire hotplugs when something has actually changed after a link
      address probe
    * Don't try to change port->connector at all on ports, just throw out
      ports that need their connectors removed to make things easier.
    
    Cc: Juston Li <juston.li@intel.com>
    Cc: Imre Deak <imre.deak@intel.com>
    Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Cc: Harry Wentland <hwentlan@amd.com>
    Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
    Reviewed-by: default avatarSean Paul <sean@poorly.run>
    Signed-off-by: default avatarLyude Paul <lyude@redhat.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-14-lyude@redhat.com
    6f85f738
drm_dp_mst_helper.h 24.1 KB