• Jani Nikula's avatar
    drm/i915: Fix DDC probe for passive adapters · 3f5f1554
    Jani Nikula authored
    Passive DP->DVI/HDMI dongles on DP++ ports show up to the system as HDMI
    devices, as they do not have a sink device in them to respond to any AUX
    traffic. When probing these dongles over the DDC, sometimes they will
    NAK the first attempt even though the transaction is valid and they
    support the DDC protocol. The retry loop inside of
    drm_do_probe_ddc_edid() would normally catch this case and try the
    transaction again, resulting in success.
    
    That, however, was thwarted by the fix for [1]:
    
    commit 9292f37e
    Author: Eugeni Dodonov <eugeni.dodonov@intel.com>
    Date:   Thu Jan 5 09:34:28 2012 -0200
    
        drm: give up on edid retries when i2c bus is not responding
    
    This added code to exit immediately if the return code from the
    i2c_transfer function was -ENXIO in order to reduce the amount of time
    spent in waiting for unresponsive or disconnected devices. That was
    possible because the underlying i2c bit banging algorithm had retries of
    its own (which, of course, were part of the reason for the bug the
    commit fixes).
    
    Since its introduction in
    
    commit f899fc64
    Author: Chris Wilson <chris@chris-wilson.co.uk>
    Date:   Tue Jul 20 15:44:45 2010 -0700
    
        drm/i915: use GMBUS to manage i2c links
    
    we've been flipping back and forth enabling the GMBUS transfers, but
    we've settled since then. The GMBUS implementation does not do any
    retries, however, bailing out of the drm_do_probe_ddc_edid() retry loop
    on first encounter of -ENXIO. This, combined with Eugeni's commit, broke
    the retry on -ENXIO.
    
    Retry GMBUS once on -ENXIO on first message to mitigate the issues with
    passive adapters.
    
    This patch is based on the work, and commit message, by Todd Previte
    <tprevite@gmail.com>.
    
    [1] https://bugs.freedesktop.org/show_bug.cgi?id=41059
    
    v2: Don't retry if using bit banging.
    
    v3: Move retry within gmbux_xfer, retry only on first message.
    
    v4: Initialize GMBUS0 on retry (Ville).
    
    v5: Take index reads into account (Ville).
    
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85924
    Cc: Todd Previte <tprevite@gmail.com>
    Cc: stable@vger.kernel.org
    Tested-by: Oliver Grafe <oliver.grafe@ge.com> (v2)
    Tested-by: default avatarJim Bride <jim.bride@linux.intel.com>
    Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
    Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
    3f5f1554
intel_i2c.c 16.9 KB