On Fri, May 05, 2017 at 03:53:39AM -0400, Sanford Rockowitz wrote: > I am the author of ddcutil (www.ddcutil.com), a Linux utility that > manages monitor settings using DDC/CI. I am seeing a pattern of user > error reports in which I2C communication is not working when a system > with a recent Intel chip, using the i915 driver, is plugged into a > docking station. Communication works when the video cable is plugged > directly into the laptop. There also seems to be a correlation with > whether a DisplayPort cable is being used (i.e. the I2C-over-aux path is > being executed), though this correlation is not as clear. Apart from the MST issues already mentioned, I have noticed (at least with some displays) that the DDC/CI slaves don't seem to do clock stretching properly, and that the default 100kHz clock tends to be too much for them. A while ago I tried to cook up some hacks to work around these issues both in our i2c and i2c-over-aux code. The idea was to just reduce the bus speed whenever DDC/CI is being attempted. My hacks are here: git://github.com/vsyrjala/linux.git i2c_bus_speed But do note that I've not seem many DP dongles that actually support the i2c bus speed control, so the usefulness of the i2c-over-aux part of that code might be a little questionable. I also didn't implement anything for the MST case, so those would still be using whatever is the default bus speed. -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
