Comment 17 for bug 1791312

From: https://kernel.ubuntu.com/~kernel-ppa/mainline/v3.15-rc2-trusty/CHANGES
I see the folowing changes for radeon:

Alex Deucher (13):
      drm/radeon/dp: handle zero sized i2c over aux transactions (v2)
      drm/dp/i2c: send bare addresses to properly reset i2c connections (v4)
      drm/dp/i2c: Update comments about common i2c over dp assumptions (v3)
      drm/radeon/dp: switch to the common i2c over aux code
      drm/radeon: fix audio pin counts for DCE6+ (v2)
      drm/radeon: disable mclk dpm on R7 260X
      drm/radeon: fix runpm handling on APUs (v4)
      drm/radeon: update CI DPM powertune settings
      drm/radeon: add support for newer mc ucode on SI (v2)
      drm/radeon: add support for newer mc ucode on CI (v2)
      drm/radeon: re-enable mclk dpm on R7 260X asics
      drm/radeon/si: make sure mc ucode is loaded before checking the size
      drm/radeon/ci: make sure mc ucode is loaded before checking the size

Christian König (2):
      drm/radeon: apply more strict limits for PLL params v2
      drm/radeon: improve PLL params if we don't match exactly v2

Christoph Jaeger (2):
      ...
      drm/radeon: fix VCE fence command

Quentin Casasnovas (1):
      drm/radeon: memory leak on bo reservation failure. v2

The:
Christian König (2):
      drm/radeon: apply more strict limits for PLL params v2
      drm/radeon: improve PLL params if we don't match exactly v2
rings a bell for me, because I believe someone somewhere was saying that a kernel parameter
speaking of PLL was fixing the problem... but people did not find PLL parameters for radeon,
so people did not follow about that comment.

From:
https://www.x.org/releases/current/doc/man/man4/radeon.4.xhtml
I see:
Option "LVDSProbePLL" "boolean"
When BIOS panel information isn’t available (like on PowerBooks), it may still be necessary to
use the firmware-provided PLL values for the panel or flickering will happen. This option will
force probing of the current value programmed in the chip when X is launched in that case.
This is only useful for LVDS panels (laptop internal panels). The default is on.
Also:
Option "DefaultTMDSPLL" "boolean"
Use the default driver provided TMDS PLL values rather than the ones provided by the BIOS.
This option has no effect on Mac cards.
Enable this option if you are having problems with a DVI monitor using the internal TMDS controller.
The default is off.

Also:
      drm/radeon: update CI DPM powertune settings
ring an other bell, because I think I remember someone saying something about DPM in some message.
Sorry for not being more specific.

A similar, older fixed closed bug:
https://bugzilla.kernel.org/show_bug.cgi?id=26552