We are using a Sabresd board (i.MX6Q) with YOCTO 4.1.15 kernel. The host supports UHS-I SDR 50 and 104 modes. However when we plug in a UHS-I SD card to usdhc3, we see that it gets detected as a "High speed device" rather than a 'ultra high speed device'. Browsing through the sources, we found that to for the SD card to work in UHS mode, the host needs to switch to 1.8v from 3.3v.
Looks like Sabresd does not support this voltage level and hence restricts this switch over.
Then, I found the following posts talk about 1.8V SD/MMC.But I failed.
What need to modify the support UHS-I mode,Also need to make some changes in u-boot.Hope to get your help.