Comment # 11 on bug 939607 from Takashi Iwai

(In reply to Peter Hanisch from comment #10)
> 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!

It tries to do some fallback, but it might have side effects.  The low
resolution problem doesn't happen if you pass dp_aux_i2c_transfer_size=4?