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f6a1906674
Sometimes we seem to get utter garbage from DPCD reads. The resulting buffer is filled with the same byte, and the operation completed without errors. My HP ZR24w monitor seems particularly susceptible to this problem once it's gone into a sleep mode. The issue seems to happen only for the first AUX message that wakes the sink up. But as the first AUX read we often do is the DPCD receiver cap it does wreak a bit of havoc with subsequent link training etc. when the receiver cap bw/lane/etc. information is garbage. A sufficient workaround seems to be to perform a single byte dummy read before reading the actual data. I suppose that just wakes up the sink sufficiently and we can just throw away the returned data in case it's crap. DP_DPCD_REV seems like a sufficiently safe location to read here. Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Todd Previte <tprevite@gmail.com> Cc: stable@vger.kernel.org Signed-off-by: Jani Nikula <jani.nikula@intel.com> |
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