(In reply to comment #8)
> first bad commit: [d1e3b5564834ea24dee6b364a172365f64865fe5] drm/radeon:
> atombios hw i2c fixes

You must have radeon.hw_i2c=1 set somewhere then.  Anyway, this is fixed in:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ffd3d3361d583cb73fa65a5fed3a196ba6f261bb