UART Subsystem

UART driver Layers in serial subsystem:
 TTY CORE
       |
 TTY Driver
        | UART/Low level
        | Hardware

•Uart Drivers revolve around three data structures.(include/linux/serial_core.h)

•Struct uart_driver

•Struct uart_port

•Struct uart_ops

•Struct console serial_omap_console

APIs

•Uart_driver_register(struct uart_driver*)

•Uart_add_one_port(uart_driver *,uart_port*);

 

UART driver

•Drivers/tty/serial/omap_serial.c

•Serial_omap_init()

{

   uart_register_driver(uart_driver *);

    platform_driver_register(serial_omap_driver);

}

static struct platform_driver serial_omap_driver = {

        .probe          = serial_omap_probe,

        .remove         = serial_omap_remove,

        .driver         = {

                .name   = DRIVER_NAME(omap-uart),

                .pm = &omap_serial_dev_pm_ops,

        },

};

• uart_register_driver(uart_driver *);

•static struct uart_driver serial_omap_reg = {

•        .owner          = THIS_MODULE,

•        .driver_name    = "OMAP-SERIAL",

•        .dev_name       = OMAP_SERIAL_NAME,

•        .nr             = OMAP_MAX_HSUART_PORTS,

•        .cons           = OMAP_CONSOLE,

•};

•During initialization, the OMAP-SERIAL driver first registers itself with the serial core using uart_register_driver()

•. When this is done, you will find a new line starting with OMAP-SERIAL in /proc/tty/drivers

•The driver_name variable should be set to something short, descriptive, and unique among all tty drivers in the kernel. This is because it shows up in the /proc/tty/drivers file to describe the driver to the user and in the sysfs tty class directory of tty drivers currently loaded

•The name field is used to define a name for the individual tty  nodes assigned to this tty driver in the /dev tree. This string is used to create a tty device by appending the number of the tty device being used at the end of the string.It is also used to create the device name in the sysfs /sys/class/tty/ directory

Platform driver

•platform_driver_register(serial_omap_driver);

•After this step, you will see two new directories appearing in sysfs, each

•corresponding to a OMAP-SERIAL port: /sys/devices/platform/omap_uart.0/

      /sys/devices/platform/omap_uart.1/ ……. /sys/devices/platform/omap_uart.3

Probe

•serial_omap_probe(struct platform_device *pdev)

   {

                 serial_omap_add_console_port(up);

      ret = uart_add_one_port(&serial_omap_reg, &up->port);

   }

Uart_add_one_port

•int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)

{

            uart_configure_port(drv, state, uport);

        /*Register the port whether it's detected or not.  This allows

         * setserial to be used to alter this ports parameters.*/

        tty_dev = tty_register_device(drv->tty_driver, uport->line, uport->dev);

}

uart_configure_port(struct uart_driver *drv, struct uart_state *state,struct uart_port *port)

{

            port->ops->config_port(port, flags);

/* If this driver supports console, and it hasn't been  successfully registered yet, try to re-register it. It may be that the port was not available.*/

                if (port->cons && !(port->cons->flags & CON_ENABLED))

                        register_console(port->cons);

}