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Imre Deak authored
Some LSPCON adaptors won't properly wake up in response to an AUX request after the adaptor was placed to a DP Sink Sleep state (via writing 0x2 to DP_SET_POWER). Based on the DP 1.4 specification 5.2.5, the sink may place the AUX CH into a low-power state while in Sleep state, but should wake it up in response to an AUX request within 1-20ms (answering with AUX defers while waking it up). As opposed to this at least the ParadTech PS175 adaptor won't fully wake in response to the first I2C-over-AUX access and will occasionally ignore the offset in I2C messages. This can result in accessing the DDC register at offset 0 regardless of the specified offset and the LSPCON detection failing. To fix this do an initial dummy read from the DPCD area. The PS175 will defer this access until it's fully woken (taking ~150ms) making sure the following I2C-over-AUX accesses will work correctly. Cc: Shashank Sharma <shashank.sharma@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Jani Nikula <jani.nikula@intel.com> Reference: https://bugs.freedesktop.org/show_bug.cgi?id=98353Signed-off-by:
Imre Deak <imre.deak@intel.com> Reviewed-by:
Shashank Sharma <shashank.sharma@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1479755707-29596-2-git-send-email-imre.deak@intel.com
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