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[Andy Whitcroft <apw@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu Trusty)
       Status: New => Fix Committed

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https://bugs.launchpad.net/bugs/1416451

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

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Trusty:
  Fix Committed

Bug description:
  [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..

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