Re: [PATCH v3 2/3] drm/i915: Don't send MST hotplugs during resume

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Jan 29, 2019 at 02:10:00PM -0500, Lyude Paul wrote:
> We have a bad habit of calling drm_fb_helper_hotplug_event() far more
> then we actually need to. MST appears to be one of these cases, where we
> call drm_fb_helper_hotplug_event() if we fail to resume a connected MST
> topology in intel_dp_mst_resume(). We don't actually need to do this at
> all though since hotplug events are already sent from
> drm_dp_connector_destroy_work() every time connectors are unregistered
> from userspace's PoV. Additionally, extra calls to
> drm_fb_helper_hotplug_event() also just mean more of a chance of doing a
> connector probe somewhere we shouldn't.
> 
> So, don't send any hotplug events during resume if the MST topology
> fails to come up. Just rely on the DP MST helpers to send them for us.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 681e88405ada..c2399acf177b 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -7096,7 +7096,10 @@ void intel_dp_mst_resume(struct drm_i915_private *dev_priv)
>  			continue;
>  
>  		ret = drm_dp_mst_topology_mgr_resume(&intel_dp->mst_mgr);
> -		if (ret)
> -			intel_dp_check_mst_status(intel_dp);
> +		if (ret) {
> +			intel_dp->is_mst = false;
> +			drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> +							false);

drm_dp_mst_topology_mgr_set_mst()
-> drm_dp_mst_topology_put_mstb()
   -> drm_dp_destroy_mst_branch_device()
      -> drm_dp_mst_topology_put_port()
         -> drm_dp_destroy_port()
	    -> drm_dp_destroy_connector_work()
	       -> drm_kms_helper_hotplug_event()

That of course requires that no one is hanging on to the
kref(s). The lifetime of the references isn't really clear
to me, but I'll take your word that it works.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> +		}
>  	}
>  }
> -- 
> 2.20.1
> 
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-- 
Ville Syrjälä
Intel