Activate i.MX internal UARTs

i.MXL (APF9328)

Nothing special to do, 2 UARTS are activated by default

i.MX27 (APF27)

On i.MX27 UART controllers pins are multiplexed with other peripheral controllers. So configuration is a little more difficult.

$ make linux26-menuconfig

Device Drivers  --->
    Character devices  --->
        Serial drivers  --->
            [*] IMX serial port support
            [*]   Console on IMX serial port
            -*-   UART1
            [ ]   UART2
            -*-   UART3
            [ ]   UART4
            [ ]   UART5
            [ ]   UART6

Some UARTs won't be available or preselected depending on the other devices configured or the baseboard used. (For example UART4 is not available on APF27Dev; indeed pins are used for USB1).

Going further

Now you have activated your serial port, you can use them: Serial ports usage on Linux