[Bug 71701] [ivb dp aux dp-to-vga dongle regression] i915 DisplayPort link training via DP-to-VGA dongle, blank screen

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=71701

--- Comment #34 from Kris Karas <bugs-a13 at moonlit-rail.com> ---
As an addendum to comment #33, it appears that the Intel X11 driver is able to
unblank the monitor roughly 50% of the time, which is statistically better than
the kernel console driver.

Running kernel 3.16, my kernel syslog is peppered with output as shown, below.  

 [drm:ironlake_disable_pch_transcoder] *ERROR* failed to disable transcoder B
 [drm:cpt_set_fifo_underrun_reporting] *ERROR* uncleared pch fifo underrun on
pch transcoder B
 [drm:cpt_serr_int_handler] *ERROR* PCH transcoder B FIFO underrun
 [drm:cpt_set_fifo_underrun_reporting] *ERROR* uncleared pch fifo underrun on
pch transcoder B
 [drm:cpt_serr_int_handler] *ERROR* PCH transcoder B FIFO underrun
 [drm:intel_dp_start_link_train] *ERROR* failed to enable link training
 [drm:intel_dp_complete_link_train] *ERROR* failed to start channel
equalization
 [drm:cpt_verify_modeset] *ERROR* mode set failed: pipe B stuck
 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 1303 at drivers/gpu/drm/i915/intel_display.c:10101
intel_modeset_check_state+0x595/0x740()
 encoder's hw state doesn't match sw tracking (expected 1, found 0)
 Modules linked in:
 CPU: 0 PID: 1303 Comm: X Tainted: G        W     3.16.3 #1
 Hardware name: Dell Inc. OptiPlex 9010/051FJ8, BIOS A08 09/19/2012
  0000000000000009 ffffffff8170cbd0 ffff8800d838fc28 ffffffff810a290d
  ffff8800d838fc90 ffff8800d838fc78 0000000000000001 ffff8800da0f1b38
  ffff8800da0f5800 ffffffff810a2977 ffffffff818e0e28 ffff880000000028
 Call Trace:
  [<ffffffff8170cbd0>] ? dump_stack+0x41/0x51
  [<ffffffff810a290d>] ? warn_slowpath_common+0x6d/0x90
  [<ffffffff810a2977>] ? warn_slowpath_fmt+0x47/0x50
  [<ffffffff813d8385>] ? intel_modeset_check_state+0x595/0x740
  [<ffffffff813d85bd>] ? intel_set_mode+0x1d/0x30
  [<ffffffff813d942f>] ? intel_crtc_set_config+0x8cf/0xd50
  [<ffffffff81378629>] ? drm_mode_set_config_internal+0x59/0xd0
  [<ffffffff8137bc00>] ? drm_mode_setcrtc+0xd0/0x560
  [<ffffffff8136d998>] ? drm_ioctl+0x178/0x580
  [<ffffffff8117ab9f>] ? do_vfs_ioctl+0x2cf/0x4b0
  [<ffffffff810cb7f7>] ? vtime_account_user+0x37/0x50
  [<ffffffff8117adb6>] ? SyS_ioctl+0x36/0x80
  [<ffffffff817155ec>] ? tracesys+0x7e/0xe2
  [<ffffffff8171564b>] ? tracesys+0xdd/0xe2
 ---[ end trace dce3bc891453170d ]---
 [drm:intel_pipe_config_compare] *ERROR* mismatch in has_dp_encoder (expected
1, found 0)

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