Comment 4 for bug 899598

To be honest i went a much cruder way that is just

static int
intel_dp_link_required(struct intel_dp *intel_dp, int pixel_clock)
{
    struct drm_crtc *crtc = intel_dp->base.base.crtc;
    struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
    int bpp = 24;

    return (pixel_clock * bpp + 9) / 10;
}

Your patch seems to be better in the sense that it correctly calculates bpp but compared to what is in upstream it checks for
if (is_edp(intel_dp))
that upstream does not anymore. I have no knowldge of the code at all so can't comment if it is correct or not. You might want to drop by #intel-gfx in freenode and talk to them, they were quite responsive when i appeared there with my issue

I'm using a Dell XPS15 outputting at 1920x1080 (without the patch resolution is limited at something like 1200xsomething)