• Lyude Paul's avatar
    drm/dp_helper: Add DP aux channel tracing · a18b2192
    Lyude Paul authored
    This is something we've needed for a very long time now, as it makes
    debugging issues with faulty MST hubs along with debugging issues
    regarding us interfacing with hubs correctly vastly easier to debug.
    Currently this can actually be done if you trace the i2c devices for DP
    using ftrace but that's significantly less useful for a couple of
    reasons:
    
    - Tracing the i2c devices through ftrace means all of the traces are
      going to contain a lot of "garbage" output that we're sending over the
      i2c line. Most of this garbage comes from retrying transactions, DRM's
      helper library adding extra transactions to work around bad hubs, etc.
    - Having a user set up ftrace so that they can provide debugging
      information is a lot more difficult then being able to say "just boot
      with drm.debug=0x100"
    - We can potentially expand upon this tracing in the future to print
      debugging information in regards to other DP transactions like MST
      sideband transactions
    
    This is inspired by a patch Rob Clark sent to do this a long time back.
    Neither of us could find the patch however, so we both assumed it would
    probably just be easier to rewrite it anyway.
    
    Cc: Rob Clark <robdclark@gmail.com>
    Signed-off-by: default avatarLyude Paul <lyude@redhat.com>
    Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    Link: https://patchwork.freedesktop.org/patch/msgid/20180716154432.13433-1-lyude@redhat.com
    a18b2192
drm_print.h 10.5 KB