[Bug 89453] 4k MST monitor doesn't come back from "xset dpms force off": failed link training

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89453

--- Comment #11 from Palmer Dabbelt <palmer at dabbelt.com> ---
This bug still exists on linux-4.1.5.  I can get my monitor to function
correctly if I apply the following patch, but I get some warnings from the
kernel during both boot and hotplug.

I don't understand how DP hotplug works on my other systems if this
intel_dp_hot_plug is empty.

Additionally, I went and printk()ed some stuff, and I never seem to have is_mst
set.  If I understand correctly, this means that I don't have an MST monitor. 
Should I change this bug's feature to "display/DP"?

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d714a4b5711e..274bd293d9e9 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4625,7 +4625,9 @@ static const struct drm_encoder_funcs intel_dp_enc_funcs
= {
 void
 intel_dp_hot_plug(struct intel_encoder *intel_encoder)
 {
-    return;
+       struct intel_dp *intel_dp = enc_to_intel_dp(&intel_encoder->base);
+
+       intel_dp_check_link_status(intel_dp);
 }

 enum irqreturn


[    4.932814] ------------[ cut here ]------------
[    4.935170] WARNING: CPU: 2 PID: 1180 at
drivers/gpu/drm/i915/intel_dp.c:4032 intel_dp_check_link_status+0x16a/0x1b0()
[    4.937557]
WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex))
[    4.937589] Modules linked in:

[    4.942308] CPU: 2 PID: 1180 Comm: kworker/2:2 Not tainted 4.1.5+ #12
[    4.944700] Hardware name: Apple Inc. MacBookPro11,2/Mac-3CBD00234E554E41,
BIOS MBP112.88Z.0138.B07.1402121134 02/12/2014
[    4.947142] Workqueue: events i915_hotplug_work_func
[    4.949583]  ffffffff81e86920 ffff88046bbcfca8 ffffffff81a1ea6d
000000000000005a
[    4.952053]  ffff88046bbcfcf8 ffff88046bbcfce8 ffffffff810ca965
ffff88046bbcfd08
[    4.954521]  ffff88046caf20e0 ffff88046c9fbb28 0000000000000001
ffff88046b487508
[    4.956989] Call Trace:
[    4.959445]  [<ffffffff81a1ea6d>] dump_stack+0x45/0x57
[    4.961915]  [<ffffffff810ca965>] warn_slowpath_common+0x85/0xc0
[    4.964389]  [<ffffffff810ca9e1>] warn_slowpath_fmt+0x41/0x50
[    4.966860]  [<ffffffff815dc70a>] intel_dp_check_link_status+0x16a/0x1b0
[    4.969342]  [<ffffffff810fc116>] ? pick_next_task_fair+0x206/0x8b0
[    4.971802]  [<ffffffff815dc760>] intel_dp_hot_plug+0x10/0x20
[    4.974251]  [<ffffffff815d21a5>] intel_ddi_hot_plug+0x25/0x30
[    4.976703]  [<ffffffff81586576>] i915_hotplug_work_func+0x1c6/0x2e0
[    4.979162]  [<ffffffff810e0af7>] process_one_work+0x147/0x3f0
[    4.981626]  [<ffffffff810e0eb9>] worker_thread+0x119/0x450
[    4.984096]  [<ffffffff810e0da0>] ? process_one_work+0x3f0/0x3f0
[    4.986574]  [<ffffffff810e5da4>] kthread+0xc4/0xe0
[    4.989053]  [<ffffffff810e5ce0>] ? kthread_create_on_node+0x180/0x180
[    4.991541]  [<ffffffff81a27f92>] ret_from_fork+0x42/0x70
[    4.994017]  [<ffffffff810e5ce0>] ? kthread_create_on_node+0x180/0x180
[    4.996552] ---[ end trace 2223e668b1c35f11 ]---

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