Behavior with 4.6.0-040600rc7-generic appears to be even saner than with
4.5.0-050400, although the AMD GPU is still not usable ("DRI_PRIME=1
glxgears" opens a black window).
Only after reporting this bug, I found that 4.5.0-050400 presented
issues with sound output in the HDMI port (sound output at a lower
sampling rate, maybe half, than it was supposed to). These issues are
fixed in 4.6.0-040600rc7-generic.
Also, 4.6.0-040600rc7-generic does not present any errors in dmesg
output when trying to use the AMD GPU (again "DRI_PRIME=1 glxgears"):
---[cut]---
[ 251.019823] [drm] PCIE GART of 2048M enabled (table at 0x0000000000040000).
[ 251.258535] [drm] ring test on 0 succeeded in 15 usecs
[ 251.258748] [drm] ring test on 1 succeeded in 14 usecs
[ 251.258787] [drm] ring test on 2 succeeded in 13 usecs
[ 251.258797] [drm] ring test on 3 succeeded in 4 usecs
[ 251.258812] [drm] ring test on 4 succeeded in 2 usecs
[ 251.258818] [drm] ring test on 5 succeeded in 2 usecs
[ 251.258824] [drm] ring test on 6 succeeded in 2 usecs
[ 251.258830] [drm] ring test on 7 succeeded in 2 usecs
[ 251.258838] [drm] ring test on 8 succeeded in 3 usecs
[ 251.258865] [drm] ring test on 9 succeeded in 6 usecs
[ 251.258878] [drm] ring test on 10 succeeded in 6 usecs
---[cut]---
Whereas 4.5.0-050400 used to output the same kind of error message presented by
xenial's 4.4 kernel ("*ERROR* amdgpu: cp failed to lock ring N (-2)"), although
the NULL pointer dereference was already fixed in 4.5.0-050400.
In short, the NULL pointer dereference is fixed upstream. With upstream
kernel, the system appears to run pretty stably using the Intel GPU as
the renderer, whereas xenial's 4.4 kernel would constantly crash.
However, the AMD GPU is still not usable even with upstream kernel, as
it renders empty (black) output.
** Tags added: kernel-fixed-upstream
** Changed in: linux (Ubuntu)
Status: Incomplete => Confirmed
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https://bugs.launchpad.net/bugs/1579374
Title:
amdgpu causes NULL pointer dereference when trying to use Topaz
(Radeon R7 M265) GPU
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