I have a Lenovo P50 and I am using Debian testing with Xorg 7.7 and Linux 4.12.
 The machine has its HDMI connector wired to the built-in NVidia card GM107GLM
(Quadro M2000M).  I am calling `xrandr --setprovideroutputsorce` to make the
connectors on the NVidia card available in my Xorg session.  On the Xorg side,
both cards are using the modesetting driver.  My DE is Gnome 3.26.

With this setup, I am seeing no tearing when I run full-screen OpenGL
applications on the internal screen.  However, when I do the same on a screen
connected via HDMI, there is tearing.  I am seeing the tearing both in my
little test application (https://git.ralfj.de/gltest.git) and when scrolling in
Firefox.