Created attachment 37912 [details]
dmesg with added WARN_ON() on atom_execute_table_locked

During Xorg shutdown, dmesg gets filled with lots of repeating:

[  101.804993] [drm:atom_op_jump] *ERROR* atombios stuck in loop for more than 5secs aborting
[  101.805045] [drm:atom_execute_table_locked] *ERROR* atombios stuck executing CD0C (len 62, WS 0, PS 0) @ 0xCD28

Xorg does NOT terminate properly until after a handful of these messages, so the system takes a long time to shutdown.

Steps to reproduce, on a Acer 5820TG (Intel Clarkdale+Radeon Evergreen switchable graphics):
1. Boot kernel with vgaswitcheroo enabled.
2. Start Xorg with no xorg.conf. Defaults to using Intel card.
3. While Xorg is running, echo OFF > /sys/kernel/debug/vgaswitcheroo/switch (powers off the Radeon card).
4. Try to quit Xorg (either by SIGTERM or Zap key sequence).

Expected result:
Xorg quits in a few seconds

Actual results:
Lots of messages on dmesg, Xorg takes minutes to die.


For convenience, I added a WARN_ON() on atom_execute_table_locked() right where it printks the above warning message. The resulting backtrace is attached.

Seemingly, drm_helper_disable_unused_functions is called by the Intel driver which ends up calling some Readeon DPMS functions (atombios_crtc_disable) which eventually try to run Atombios code while rdev->powered_down is TRUE. 

A trivial workaround is to patch atombios_crtc_disable and do nothing if rdev->powered_down is TRUE. That works for me but I don't really know if it's exactly the ideal solution.