• Ville Syrjälä's avatar
    drm/i915: Assume non-DP++ port if dvo_port is HDMI and there's no AUX ch specified in the VBT · bc9db5ad
    Ville Syrjälä authored
    My heuristic for detecting type 1 DVI DP++ adaptors based on the VBT
    port information apparently didn't survive the reality of buggy VBTs.
    In this particular case we have a machine with a natice HDMI port, but
    the VBT tells us it's a DP++ port based on its capabilities.
    
    The dvo_port information in VBT does claim that we're dealing with a
    HDMI port though, but we have other machines which do the same even
    when they actually have DP++ ports. So that piece of information alone
    isn't sufficient to tell the two apart.
    
    After staring at a bunch of VBTs from various machines, I have to
    conclude that the only other semi-reliable clue we can use is the
    presence of the AUX channel in the VBT. On this particular machine
    AUX channel is specified as zero, whereas on some of the other machines
    which listed the DP++ port as HDMI have a non-zero AUX channel.
    
    I've also seen VBTs which have dvo_port a DP but have a zero AUX
    channel. I believe those we need to treat as DP ports, so we'll limit
    the AUX channel check to just the cases where dvo_port is HDMI.
    
    If we encounter any more serious failures with this heuristic I think
    we'll have to have to throw it out entirely. But that could mean that
    there is a risk of type 1 DVI dongle users getting greeted by a
    black screen, so I'd rather not go there unless absolutely necessary.
    
    v2: Remove the duplicate PORT_A check (Daniel)
        Fix some typos in the commit message
    
    Cc: Daniel Otero <daniel.otero@outlook.com>
    Cc: stable@vger.kernel.org
    Tested-by: default avatarDaniel Otero <daniel.otero@outlook.com>
    Fixes: d6199256 ("drm/i915: Determine DP++ type 1 DVI adaptor presence based on VBT")
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97994Signed-off-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
    Link: http://patchwork.freedesktop.org/patch/msgid/1478884464-14251-1-git-send-email-ville.syrjala@linux.intel.comReviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    (cherry picked from commit 7a17995a)
    Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
    bc9db5ad
intel_bios.c 48.9 KB