• Ville Syrjälä's avatar
    drm/i915/hdmi: Ignore DP++ TMDS clock limit for native HDMI ports · c2696280
    Ville Syrjälä authored
    Lots of machines these days seem to have a crappy type1 DP dual
    mode adaptor chip slapped onto the motherboard. Based on the
    DP dual mode spec we currently limit those to 165MHz max TMDS
    clock.
    
    Windows OTOH ignores DP dual mode adaptors when the VBT
    indicates that the port is not actually DP++, so we can
    perhaps assume that the vendors did intend that the 165MHz
    clock limit doesn't apply here. Though it would be much
    nicer if they actually declared an explicit limit through
    VBT, but that doesn't seem to be happening either.
    
    So in order to match Windows behaviour let's ignore the
    DP dual mode adaptor's TMDS clock limit for ports that
    don't look like DP++ in VBT.
    
    Unfortunately many older VBTs misdelcare their DP++ ports
    as just HDMI (eg. ILK Dell Latitude E5410) or DP (eg. SNB
    Lenovo ThinkPad X220). So we can't really do this universally
    without risking black screens. I suppose a sensible cutoff
    is HSW+ since that's when 4k became a thing and one might
    assume that the machines have been tested to work with higher
    TMDS clock rates.
    
    v2: s/IS_BROADWELL/IS_HASWELL/
    Acked-by: default avatarJani Nikula <jani.nikula@intel.com>
    Signed-off-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20211222161738.12478-1-ville.syrjala@linux.intel.com
    c2696280
intel_hdmi.c 93.1 KB