FAILED: patch "[PATCH] drm/i915: Fix intel_dp_mst_best_encoder()" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 4bbf0d4749e707b6b262d576a9a9ef5c63b52dd4 Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@redhat.com>
Date: Mon, 8 Oct 2018 19:24:34 -0400
Subject: [PATCH] drm/i915: Fix intel_dp_mst_best_encoder()

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
(cherry picked from commit a9f9ca33d1fe9325f414914be526c0fc4ba5281c)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 0f14c0d1669c..7f155b4f1a7d 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -404,8 +404,6 @@ 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;
 }