serial: sh-sci: Add more Serial Mode Register documentation

static void sci_set_termios(struct uart_port *port, struct ktermios *termios,

			    struct ktermios *old)

{

	unsigned int baud, smr_val = 0, scr_val = 0, i;

	unsigned int baud, smr_val = SCSMR_ASYNC, scr_val = 0, i;

	unsigned int brr = 255, cks = 0, srr = 15, dl = 0, sccks = 0;

	unsigned int brr1 = 255, cks1 = 0, srr1 = 15, dl1 = 0;

	struct sci_port *s = to_sci_port(port);

/* SCSMR (Serial Mode Register) */

#define SCSMR_C_A	BIT(7)	/* Communication Mode */

#define SCSMR_CSYNC	BIT(7)	/*   - Clocked synchronous mode */

#define SCSMR_ASYNC	0	/*   - Asynchronous mode */

#define SCSMR_CHR	BIT(6)	/* 7-bit Character Length */

#define SCSMR_PE	BIT(5)	/* Parity Enable */

#define SCSMR_ODD	BIT(4)	/* Odd Parity */

#define SCSMR_STOP	BIT(3)	/* Stop Bit Length */

#define SCSMR_CKS	0x0003	/* Clock Select */

/* Serial Mode Register, SCIFA/SCIFB only bits */

#define SCSMR_CKEDG	BIT(12)	/* Transmit/Receive Clock Edge Select */

#define SCSMR_SRC_MASK	0x0700	/* Sampling Control */

#define SCSMR_SRC_16	0x0000	/* Sampling rate 1/16 */

#define SCSMR_SRC_5	0x0100	/* Sampling rate 1/5 */

#define SCSMR_SRC_7	0x0200	/* Sampling rate 1/7 */

#define SCSMR_SRC_11	0x0300	/* Sampling rate 1/11 */

#define SCSMR_SRC_13	0x0400	/* Sampling rate 1/13 */

#define SCSMR_SRC_17	0x0500	/* Sampling rate 1/17 */

#define SCSMR_SRC_19	0x0600	/* Sampling rate 1/19 */

#define SCSMR_SRC_27	0x0700	/* Sampling rate 1/27 */

/* Serial Control Register, SCIFA/SCIFB only bits */

#define SCSCR_TDRQE	BIT(15)	/* Tx Data Transfer Request Enable */

#define SCSCR_RDRQE	BIT(14)	/* Rx Data Transfer Request Enable */