Comment 16 for bug 1765363

@Alain What's you graphics card?
nouveau.runpm=-1 is the default setting for nouveau on Optimus systems. If the graphics card is not used, it will be powered down after 5 seconds iirc. As you did, this can be forced in the kernel boot parameters.
Unfortunately, with this setting, systems with recent graphics cards (GTX 10xx series) will not reach a usable desktop after login, and end up with a black screen.
I couldn't confirm but it may be this bug: https://bugs.freedesktop.org/show_bug.cgi?id=100228

With nouveau.runpm=0, I experience slowdowns and lockups even if the Intel iGPU is in use, so some other nouveau bug might be involved.