Per Matias Edlund: I recently used the tcflush function and found that it...

Per Matias Edlund:  I recently used the tcflush function and found that it failed with ENOTTY. The reason is that the TCFLSH case in the function uart_ioctl in the file drivers/serial/serial.c does not update the ret value."  On success, the TCFLSH IOCTL logic needs to explicitly set the return value (ret) to zero.