https://bugs.freedesktop.org/show_bug.cgi?id=102800
--- Comment #7 from higuita@gmx.net --- I tried to downgrade the kernel to 4.11, 4.10 and 4.9 and i failed to enable DRI_PRIME on the dedicated card, always with the same error. I then tried to downgrade the mesa and libdrm to the distro original version and also, failed to enabled the card...
So yes, the card worked in the past with DynPwr, but now i'm unable to enable it... Maybe some other update, firmware, whatever is also messing this. I do recall being able to boot one older kernel and have the card working, but booting with the more recent, it failed... all this around june
I will try to boot from a liveCD, to try to get it working again and try to understand what else is causing this.
Anyway, using runpm=0 works and the problems seems to be always with the kernel/atombios being unable to re-enable the card after shut it down