Comment # 10 on bug 939607 from Peter Hanisch

Applying your patch to the current 4.1.4 kernel and starting without specifying
drm_kms_helper.dp_aux_i2c_transfer_size works, i.e. the external monitor/dongle
show up correctly.

However, unlike the kernel parameter, it seems the resolution on the external
monitor during boot and on the (kdm) login screen seems to be off. My external
monitor has a native resolution of 1400x1050, but everything before logging in
looks more like 1024x768 or some such. Nevertheless, it fixes the original
problem!