Comment 74 for bug 1034002

Same issue for my A8-450M laptop with Integrated or Discrete GPU set.
I made some tests from kernel 3.8.0 to 3.12-RC6 on Ubuntu.
I got same result with other distro like ArchLinux or Fedora.

# lspci
00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 15h (Models 10h-1
fh) Processor Root Complex
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Trinit
y [Radeon HD 7640G]

Some other tests on my main kernel 3.11.6 (Ubuntu PPA)
(CPU and GPU firmware has been updated to latest version)

 - After suspend and resume, with ssh I can check brightness control on /sys/class/blacklight/radeon_bl0/brightness and change the value but nothing change on screen (always black screen)
 - no syslog entry give information on the problem
 - no more information with drm.debug on kernel
 - fglrx doesn't have the same problem, suspend and resume work fine
   (but fglrx don't allow to change brightness).

So, this concern seems to come from the drm driver and not from kernel or acpi,
but I don't have enough knowledge to go further to identify the root cause in xorg