My m3800 has a Realtek RTS5249 in it, and whenever I insert an SD card, I get this in my dmesg output:
[ 2087.665790] mmc0: card never left busy state[ 2087.665795] mmc0: error -110 whilst initialising SD card
If I plug in an external card reader, the SD cards all work great, but not on the internal reader.
I'm running Ubuntu 15.10 and have the newer hardware model with thunderbolt support.
When debugging these types of errors it's always used to know: did the card reader work before for you? For example, did it work on Ubuntu 15.04? This helps determine whether the problem is likely hardware or software.
Also are you using the default kernel for 15.10?
I've only had this laptop a little over a month and it's the first time I've tried to use it. It's only ever had Ubuntu 15.10 on it (it shipped with Windows and I've manually installed Ubuntu on it).
Yes, default kernel, 4.2.0-19-generic