We have a critical problem with imx28. We use Telit HE910 module for GSM and GPS, it has 7 ACM interface under /dev/ directory and /dev/ttyACM0 is for GSM, /dev/ttyACM2 is for GPS. When we opened any 2 ports of /dev/ttyACMx, cpu is blocked for a few milliseconds. Because of imx28 has 16 bytes uart fifo, data loss would occur. The funny part is that there is no transfer, no read/write request on /dev/ttyACMx's, only opened any 2 of them.