[Bug 107546] Screen is frozen on second connection of DP MST dock

Tue Nov 13 23:35:41 UTC 2018

https://bugs.freedesktop.org/show_bug.cgi?id=107546

--- Comment #34 from VF <vedran.furac at gmail.com> ---
Hello,

I think I have the same issue on Intel's NUC7i5BNB with dual Dell monitors
using daisy chain (and 3rd over HDMI). I've tested many kernels and have come
to conclusion the the problem was first introduced in 4.11 and various
manifestation of it appear in all subsequent kernels up to 4.19-rc7 from
Debian. Kernels 4.9 and 4.10 work fine.

To reproduce it, all I need to do is switch input using primary Dell OSD from
DP to mDP (nothing on it) and then switch back to DP input. This results in
flood of:

[1615629.735590] [drm:intel_ddi_prepare_link_retrain [i915]] *ERROR* Timeout
waiting for DDI BUF C idle bit
[1615629.811616] [drm:intel_dp_start_link_train [i915]] *ERROR* Timed out
waiting for DP idle patterns

messages and the X server is frozen. SSH works normally, but if I try to
restart X, system usually hard locks and I need to cut the power (not even
sysrq magic works). I was unable to find any workarounds. With 4.18 there's
even kernel oops (after returning to DP input):

[  321.495462] [drm:intel_dp_check_mst_status [i915]] got esi 42 10 00
[  321.497662] BUG: unable to handle kernel NULL pointer dereference at
0000000000000000
[  321.497665] PGD 0 P4D 0 
[  321.497667] Oops: 0000 [#1] SMP NOPTI
[  321.497669] CPU: 1 PID: 188 Comm: kworker/u8:3 Tainted: G     U     O     
4.18.0-2-amd64 #1 Debian 4.18.10-2
[  321.497670] Hardware name:  /NUC7i5BNB, BIOS
BNKBL357.86A.0049.2017.0724.1541 07/24/2017
[  321.497689] Workqueue: i915-dp i915_digport_work_func [i915]
[  321.497692] RIP: 0010:refcount_inc_not_zero+0x0/0x50
[  321.497693] Code: c0 74 02 f3 c3 80 3d 64 bb d3 00 00 75 f5 48 c7 c7 70 9a
07 84 c6 05 54 bb d3 00 01 e8 f9 f3 cb ff 0f 0b c3 66 0f 1f 44 00 00 <8b> 07 85
c0 8d 50 01 74 35 85 d2 74 0b f0 0f b1 17 75 ef 83 fa ff 
[  321.497712] RSP: 0018:ffffa1f8c37c7d18 EFLAGS: 00010246
[  321.497713] RAX: 0000000000000000 RBX: ffff935493b129c8 RCX:
0000000000000000
[  321.497714] RDX: ffff93549270bd00 RSI: 0000000000000001 RDI:
0000000000000000
[  321.497715] RBP: 0000000000000000 R08: 00000000fffffffa R09:
0000000000000002
[  321.497716] R10: ffffa1f8c37c7cf0 R11: 0000000000000102 R12:
ffff935493b12870
[  321.497717] R13: 0000000000000001 R14: ffffa1f8c37c7dc2 R15:
ffff935493b12700
[  321.497718] FS:  0000000000000000(0000) GS:ffff9354be880000(0000)
knlGS:0000000000000000
[  321.497720] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  321.497721] CR2: 0000000000000000 CR3: 00000001dda0a001 CR4:
00000000003606e0
[  321.497722] Call Trace:
[  321.497725]  refcount_inc+0x5/0x30
[  321.497730]  drm_dp_get_mst_branch_device+0xc2/0xe0 [drm_kms_helper]
[  321.497735]  drm_dp_mst_hpd_irq+0x104/0x8c0 [drm_kms_helper]
[  321.497750]  ? intel_dp_check_mst_status+0xba/0x1e0 [i915]
[  321.497763]  intel_dp_check_mst_status+0xba/0x1e0 [i915]
[  321.497776]  intel_dp_hpd_pulse+0x176/0x2e0 [i915]
[  321.497778]  ? __switch_to_asm+0x40/0x70
[  321.497791]  i915_digport_work_func+0x8f/0x120 [i915]
[  321.497794]  process_one_work+0x195/0x370
[  321.497795]  worker_thread+0x30/0x390
[  321.497797]  ? process_one_work+0x370/0x370
[  321.497799]  kthread+0x113/0x130
[  321.497800]  ? kthread_create_worker_on_cpu+0x70/0x70
[  321.497802]  ret_from_fork+0x35/0x40

I'll attach full debug output.

Regards,
Vedran

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