During modeset cleanup on driver unload we may have a pending
hotplug work. This needs to be canceled early during the teardown
so that it does not fire after we have freed the connector.
We do this after drm_kms_helper_poll_fini(dev) since this might
trigger modeset retry work due to link retrain and before
intel_fbdev_fini() since this work requires the lock from fbdev.

If this is not done we may see something like:
DEBUG_LOCKS_WARN_ON(mutex_is_locked(lock))
 ------------[ cut here ]------------
 WARNING: CPU: 4 PID: 5010 at kernel/locking/mutex-debug.c:103 mutex_destroy+0x4e/0x60
 Modules linked in: i915(-) snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec snd_hwdep snd_hda_core snd_pcm vgem ax88179_178
+a usbnet mii x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel e1000e ptp pps_core prime_numbers i2c_hid
+[last unloaded: snd_hda_intel]
 CPU: 4 PID: 5010 Comm: drv_module_relo Tainted: G     U          4.14.0-rc3-CI-CI_DRM_3186+ #1
 Hardware name: Intel Corporation CoffeeLake Client Platform/CoffeeLake S UDIMM RVP, BIOS CNLSFWX1.R00.X104.A03.1709140524 09/14/2017
 task: ffff8803c827aa40 task.stack: ffffc90000520000
 RIP: 0010:mutex_destroy+0x4e/0x60
 RSP: 0018:ffffc90000523d58 EFLAGS: 00010292
 RAX: 000000000000002a RBX: ffff88044fbef648 RCX: 0000000000000000
 RDX: 0000000080000001 RSI: 0000000000000001 RDI: ffffffff810f0cf0
 RBP: ffffc90000523d60 R08: 0000000000000001 R09: 0000000000000001
 R10: 000000000f21cb81 R11: 0000000000000000 R12: ffff88044f71efc8
 R13: ffffffffa02b3d20 R14: ffffffffa02b3d90 R15: ffff880459b29308
 FS:  00007f5df4d6e8c0(0000) GS:ffff88045d300000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000055ec51f00a18 CR3: 0000000451782006 CR4: 00000000003606e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  drm_fb_helper_fini+0xd9/0x130
  intel_fbdev_destroy+0x12/0x60 [i915]
  intel_fbdev_fini+0x28/0x30 [i915]
  intel_modeset_cleanup+0x45/0xa0 [i915]
  i915_driver_unload+0x92/0x180 [i915]
  i915_pci_remove+0x19/0x30 [i915]
  i915_driver_unload+0x92/0x180 [i915]
  i915_pci_remove+0x19/0x30 [i915]
  pci_device_remove+0x39/0xb0
  device_release_driver_internal+0x15d/0x220
  driver_detach+0x40/0x80
  bus_remove_driver+0x58/0xd0
  driver_unregister+0x2c/0x40
  pci_unregister_driver+0x36/0xb0
  i915_exit+0x1a/0x8b [i915]
  SyS_delete_module+0x18c/0x1e0
  entry_SYSCALL_64_fastpath+0x1c/0xb1
 RIP: 0033:0x7f5df3286287
 RSP: 002b:00007fff8e107cc8 EFLAGS: 00000246 ORIG_RAX: 00000000000000b0
 RAX: ffffffffffffffda RBX: ffffffff81493a03 RCX: 00007f5df3286287
 RDX: 0000000000000001 RSI: 0000000000000800 RDI: 0000564c7be02e48
 RBP: ffffc90000523f88 R08: 0000000000000000 R09: 0000000000000080
 R10: 00007f5df4d6e8c0 R11: 0000000000000246 R12: 0000000000000000
 R13: 00007fff8e107eb0 R14: 0000000000000000 R15: 0000000000000000
Or a GPF like:

 general protection fault: 0000 [#1] PREEMPT SMP
 Modules linked in: i915(-) snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec snd_hwdep snd_hda_core snd_pcm vgem ax88179_178
+a usbnet mii x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel e1000e ptp pps_core prime_numbers i2c_hid
+[last unloaded: snd_hda_intel]
 CPU: 0 PID: 82 Comm: kworker/0:1 Tainted: G     U  W       4.14.0-rc3-CI-CI_DRM_3186+ #1
 Hardware name: Intel Corporation CoffeeLake Client Platform/CoffeeLake S UDIMM RVP, BIOS CNLSFWX1.R00.X104.A03.1709140524 09/14/2017
 Workqueue: events intel_dp_modeset_retry_work_fn [i915]
 task: ffff88045a5caa40 task.stack: ffffc90000378000
 RIP: 0010:drm_setup_crtcs+0x143/0xbf0
 RSP: 0018:ffffc9000037bd20 EFLAGS: 00010202
 RAX: 6b6b6b6b6b6b6b6b RBX: 0000000000000002 RCX: 0000000000000001
 RDX: 0000000000000001 RSI: 0000000000000780 RDI: 00000000ffffffff
 RBP: ffffc9000037bdb8 R08: 0000000000000001 R09: 0000000000000001
 R10: 0000000000000780 R11: 0000000000000000 R12: 0000000000000002
 R13: ffff88044fbef4e8 R14: 0000000000000780 R15: 0000000000000438
 FS:  0000000000000000(0000) GS:ffff88045d200000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000055ec51ee5168 CR3: 000000044c89d003 CR4: 00000000003606f0
 Call Trace:
  drm_fb_helper_hotplug_event.part.18+0x7e/0xc0
  drm_fb_helper_hotplug_event+0x1a/0x20
  intel_fbdev_output_poll_changed+0x1a/0x20 [i915]
  drm_kms_helper_hotplug_event+0x27/0x30
  intel_dp_modeset_retry_work_fn+0x77/0x80 [i915]
  process_one_work+0x233/0x660
  worker_thread+0x206/0x3b0
  kthread+0x152/0x190
  ? process_one_work+0x660/0x660
  ? kthread_create_on_node+0x40/0x40
  ret_from_fork+0x27/0x40
 Code: 06 00 00 45 8b 45 20 31 db 45 31 e4 45 85 c0 0f 8e 91 06 00 00 44 8b 75 94 44 8b 7d 90 49 8b 45 28 49 63 d4 44 89 f6 41 83 c4 01 <48> 8b 04 d0 44
+89 fa 48 8b 38 48 8b 87 a8 01 00 00 ff 50 20 01
 RIP: drm_setup_crtcs+0x143/0xbf0 RSP: ffffc9000037bd20
 ---[ end trace 08901ff1a77d30c7 ]---

v2:
* Rename it to intel_hpd_poll_fini() and call drm_kms_helper_fini() inside it
as the first step before cancel work (Chris Wilson)
* Add GPF trace in commit message and make the function static (Maarten Lankhorst)
Suggested-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: 9301397a ("drm/i915: Implement Link Rate fallback on Link training failure")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tony Cheng <tony.cheng@amd.com>
Cc: Harry Wentland <Harry.wentland@amd.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1509054720-25325-1-git-send-email-manasi.d.navare@intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>