Comment # 12 on bug 76490 from Gustavo Lopes

I tried sprinkling si_dpm_ini() and si_dpm_enabled with printk and msleep
statements, but while I can tell they're being executed (it takes much longer
for the screen to become black due to the sleeps), I cannot see any log
messages. The last lines I see are:

[drm] radeon kernel modesetting enabled.
fb: switching to radeondrmfb from EFI VGA