Comment 110 for bug 1871721

0519c102f5285476d7868a387bdb6c58385e4074 is the first bad commit
commit 0519c102f5285476d7868a387bdb6c58385e4074
Author: Ville Syrjälä <email address hidden>
Date: Mon Jan 22 19:41:31 2018 +0200

    drm/i915: Implement display w/a #1143

    Apparently SKL/KBL/CFL need some manual help to get the
    programmed HDMI vswing to stick. Implement the relevant
    workaround (display w/a #1143).

    Note that the relevant chicken bits live in a transcoder register
    even though the bits affect a specific DDI port rather than a
    specific transcoder. Hence we must pick the correct transcoder
    register instance based on the port rather than based on the
    cpu_transcoder.

    Also note that for completeness I included support for DDI A/E
    in the code even though we never have HDMI on those ports.

    v2: CFL needs the w/a as well (Rodrigo and Art)

    Cc: Rodrigo Vivi <email address hidden>
    Cc: Art Runyan <email address hidden>
    Signed-off-by: Ville Syrjälä <email address hidden>
    Link: https://patchwork.<email address hidden>
    Reviewed-by: Rodrigo Vivi <email address hidden>