Can't switch display mode more than one cycle when docked

[Timo Aaltonen]

[Impact]
We have a system under certification that needs a workaround in the kernel for now. The bug is that if the machine is booted attached to a dock with a monitor connected to it's VGA output, the connection to the monitor is dropped after one full cycle of display modes with the hotkey combo. This is a firmware bug and will eventually be fixed by the BIOS vendor, but in the meantime we need a workaround in the kernel.

The dock has a builtin DP-VGA dongle which is the culprit here.

[Test Case]
attach the unit to a doc with a monitor plugged to a VGA port, switch display modes with hotkey combo, should be able to do more than one cycle with the combo

[Regression Potential]
We got the patch from Intel, with this disclaimer:
"The workaround in comment 41# maybe has side effect on DP port which doesn't connect DP screen. On these DP ports, this workaround will add an extra power on and power off command . So this workaround couldn't push to upstream."

so there shouldn't be any visible regressions..

[Brad Figg (brad-figg)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-trusty' to 'verification-done-trusty'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 3.13.0-46.75

---------------
linux (3.13.0-46.75) trusty; urgency=low

  [ Seth Forshee ]

  * Release Tracking Bug
    - LP: #1419963

  [ Andy Whitcroft ]

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  * hyper-v -- fix comment handing in /etc/network/interfaces
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  [ Kamal Mostafa ]

  * [Packaging] force "dpkg-source -I -i" behavior

  [ Upstream Kernel Changes ]

  * Revert "[SCSI] mpt2sas: Remove phys on topology change."
    - LP: #1419838
  * Revert "[SCSI] mpt3sas: Remove phys on topology change"
    - LP: #1419838
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    - LP: #1413129
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    - LP: #1404558, #1419837
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    mapping
    - LP: #1419837
  * userns: Document what the invariant required for safe unprivileged
    mappings.
    - LP: #1419837
  * userns: Only allow the creator of the userns unprivileged mappings
    - LP: #1419837
  * x86_64, switch_to(): Load TLS descriptors before switching DS and ES
    - LP: #1419837
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    - LP: #1419837
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    - LP: #1419837
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    - LP: #1419837
  * x86_64, vdso: Fix the vdso address randomization algorithm
    - LP: #1419837
  * groups: Consolidate the setgroups permission checks
    - LP: #1419837
  * userns: Don't allow setgroups until a gid mapping has been setablished
    - LP: #1419837
  * userns: Don't allow unprivileged creation of gid mappings
    - LP: #1419837
  * move d_rcu from overlapping d_child to overlapping d_alias
    - LP: #1419837
  * deal with deadlock in d_walk()
    - LP: #1419837
  * Linux 3.13.11-ckt14
    - LP: #1419837
  * gre: fix the inner mac header in nbma tunnel xmit path
    - LP: #1419838
  * netlink: Always copy on mmap TX.
    - LP: #1419838
  * netlink: Don't reorder loads/stores before marking mmap netlink frame
    as available
    - LP: #1419838
  * in6: fix conflict with glibc
    - LP: #1419838
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    interrupts
    - LP: #1419838
  * batman-adv: Unify fragment size calculation
    - LP: #1419838
  * batman-adv: avoid NULL dereferences and fix if check
    - LP: #1419838
  * net: Fix stacked vlan offload features computation
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    - L...