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[Bug 1479136] Re: [ubuntu 14.04.2] Artefacts in radeon driver on kernel 3.16 and upwards


OK, about the bisect:

c2fb3094669a3205f16a32f4119d0afe40b1a1fd is the first bad commit
Date:   Sun Apr 20 13:24:32 2014 +0200

    drm/radeon: improve PLL limit handling in post div calculation
    This improves the PLL parameters when we work at
    the limits of the allowed ranges.

I reverted this commit (I got some good working tips from Chris
Bainbridge), tested the result with the kernels 4.4.0-rc1 and 4.6.0-rc6+
and the problem is completely gone. I ended up with a good stable and
rock-solid display output without artefacts.

I could test against some other kernels if any of the devs here would
like me to do that.

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  [ubuntu 14.04.2] Artefacts in radeon driver on kernel 3.16 and upwards

Status in linux package in Ubuntu:

Bug description:
  Ubuntu-Mate 14.04.2

  This is what I get if I run a kernel newer than 3.13: https://www.youtube.com/watch?v=nx2-Fvihzxg
  sorry for the link, I just don't know how to describe these artefacts verbally.
  (a storm of small horizontal moving blips from right to left ??)

  Those artefacts appear as soon as new kernel is selected in GRUB, and
  remain during the whole session.

  The lastest kernel (from the main repository that is) working without
  artifacts is v3.13.0.59. All later kernels have artifacts. All later
  kernels also are either "-utopic" or "-vivid" instead of "-trusty",
  but I do not know if it is related.

  GPU: Mobility Radeon HD 3200 (RS780M)
  System: Ubuntu Mate 14.04.2  32-bit

  Kernels tested: (and earlier) , , 
  Only (and earlier) are without problems.

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