drm/i915: Fix intel_dp_mst_best_encoder()

BugLink: https://bugs.launchpad.net/bugs/1844558
[ Upstream commit a9f9ca33d1fe9325f414914be526c0fc4ba5281c ]

Currently, i915 appears to rely on blocking modesets on
no-longer-present MSTB ports by simply returning NULL for
->best_encoder(), which in turn causes any new atomic commits that don't
disable the CRTC to fail. This is wrong however, since we still want to
allow userspace to disable CRTCs on no-longer-present MSTB ports by
changing the DPMS state to off and this still requires that we retrieve
an encoder.

So, fix this by always returning a valid encoder regardless of the state
of the MST port.

Changes since v1:
- Remove mst atomic helper, since this got replaced with a much simpler
  solution

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20181008232437.5571-6-lyude@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 37878f27191ed86095d986972ca708c7d116959c..e49b702675d61c98f24fdf3fcd0feb817ea7758a 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -410,8 +410,6 @@ static struct drm_encoder *intel_mst_atomic_best_encoder(struct drm_connector *c
        struct intel_dp *intel_dp = intel_connector->mst_port;
        struct intel_crtc *crtc = to_intel_crtc(state->crtc);
 
-       if (!READ_ONCE(connector->registered))
-               return NULL;
        return &intel_dp->mst_encoders[crtc->pipe]->base.base;
 }