serial: Create uart_xmit_advance()

/* number of characters left in xmit buffer before we ask for more */

#define WAKEUP_CHARS		256

/**

 * uart_xmit_advance - Advance xmit buffer and account Tx'ed chars

 * @up: uart_port structure describing the port

 * @chars: number of characters sent

 *

 * This function advances the tail of circular xmit buffer by the number of

 * @chars transmitted and handles accounting of transmitted bytes (into

 * @up's icount.tx).

 */

static inline void uart_xmit_advance(struct uart_port *up, unsigned int chars)

{

	struct circ_buf *xmit = &up->state->xmit;

	xmit->tail = (xmit->tail + chars) & (UART_XMIT_SIZE - 1);

	up->icount.tx += chars;

}

struct module;

struct tty_driver;