Yes, Jimmy, you are right. I change code(mx6q_sabresd.c, setup_uart) from:
mxc_iomux_v3_setup_pad(MX6Q_PAD_CSI0_DAT10__UART1_TXD);
mxc_iomux_v3_setup_pad(MX6Q_PAD_CSI0_DAT11__UART1_RXD);
to
mxc_iomux_v3_setup_pad(MX6Q_PAD_SD3_DAT7__UART1_TXD);
mxc_iomux_v3_setup_pad(MX6Q_PAD_SD3_DAT6__UART1_RXD);
Now I get message from UART. It then stopped at "MMC", but anyway it show something.
Thanks!