XPS13 SD card reader not working

I received my XPS13 9350 developer's edition from Dell last week. After a few problems getting everything installed, I now have it working well. It's running Xenial Ubuntu. I had to upgrade to a newer kernel (4.6) since the Xenial stock kernel (4.4) had screen flickering and palm detection wasn't working. 

I now have a new problem. The SD card doesn't appear to work. I can see it using the output of lspci:

3b:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS525A PCI Express Card Reader [10ec:525a] (rev 01) Subsystem: Dell RTS525A PCI Express Card Reader [1028:0704] Kernel driver in use: rtsx_pci Kernel modules: rtsx_pci

Also, lshw:

*-generic
       description: Unassigned class
       product: Realtek Semiconductor Co., Ltd.
       vendor: Realtek Semiconductor Co., Ltd.
       physical id: 0
       bus info: pci@0000:3b:00.0
       version: 01
       width: 32 bits
       clock: 33MHz
       capabilities: bus_master cap_list
       configuration: driver=rtsx_pci latency=0
       resources: irq:276 memory:dc100000-dc100fff

Note that three additional capabilities, pm msi pciexpress, appear when running sudo lshw. Interestingly, I don't see anything under devices that looks like what I would expect (e.g., /dev/mmc*).

I'm a bit stumped as to what to do here. I posted a thread on askubuntu with no success. Is it possible it's a hardware issue rather than a Linux driver issue? If so, what's the best way to test this? Is there a BIOS option or boot disk I could use for testing?