serial: ucc_uart: Remove custom frame size calculation

The number of bits can be calculated using tty_get_frame_size(), no
need for the driver to do it on its own.

Also remove a comment on number of bits that doesn't match the code nor
the comment on ucc_uart_pram's rx_length ("minus 1" part differs). That
comment seems a verbatim copy of that in cpm_uart/cpm_uart_core.c
anyway so perhaps it was just copied over w/o much thinking.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220830084925.5608-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/ucc_uart.c

@@ -854,13 +854,6 @@ static void qe_uart_set_termios(struct uart_port *port,
 	u16 upsmr = ioread16be(&uccp->upsmr);
 	struct ucc_uart_pram __iomem *uccup = qe_port->uccup;
 	u16 supsmr = ioread16be(&uccup->supsmr);
-	u8 char_length = 2; /* 1 + CL + PEN + 1 + SL */
-
-	/* Character length programmed into the mode register is the
-	 * sum of: 1 start bit, number of data bits, 0 or 1 parity bit,
-	 * 1 or 2 stop bits, minus 1.
-	 * The value 'bits' counts this for us.
-	 */
 
 	/* byte size */
 	upsmr &= UCC_UART_UPSMR_CL_MASK;
@@ -870,22 +863,18 @@ static void qe_uart_set_termios(struct uart_port *port,
 	case CS5:
 		upsmr |= UCC_UART_UPSMR_CL_5;
 		supsmr |= UCC_UART_SUPSMR_CL_5;
-		char_length += 5;
 		break;
 	case CS6:
 		upsmr |= UCC_UART_UPSMR_CL_6;
 		supsmr |= UCC_UART_SUPSMR_CL_6;
-		char_length += 6;
 		break;
 	case CS7:
 		upsmr |= UCC_UART_UPSMR_CL_7;
 		supsmr |= UCC_UART_SUPSMR_CL_7;
-		char_length += 7;
 		break;
 	default:	/* case CS8 */
 		upsmr |= UCC_UART_UPSMR_CL_8;
 		supsmr |= UCC_UART_SUPSMR_CL_8;
-		char_length += 8;
 		break;
 	}
 
@@ -893,13 +882,11 @@ static void qe_uart_set_termios(struct uart_port *port,
 	if (termios->c_cflag & CSTOPB) {
 		upsmr |= UCC_UART_UPSMR_SL;
 		supsmr |= UCC_UART_SUPSMR_SL;
-		char_length++;  /* + SL */
 	}
 
 	if (termios->c_cflag & PARENB) {
 		upsmr |= UCC_UART_UPSMR_PEN;
 		supsmr |= UCC_UART_SUPSMR_PEN;
-		char_length++;  /* + PEN */
 
 		if (!(termios->c_cflag & PARODD)) {
 			upsmr &= ~(UCC_UART_UPSMR_RPM_MASK |
@@ -954,7 +941,7 @@ static void qe_uart_set_termios(struct uart_port *port,
 	iowrite16be(upsmr, &uccp->upsmr);
 	if (soft_uart) {
 		iowrite16be(supsmr, &uccup->supsmr);
-		iowrite8(char_length, &uccup->rx_length);
+		iowrite8(tty_get_frame_size(termios->c_cflag), &uccup->rx_length);
 
 		/* Soft-UART requires a 1X multiplier for TX */
 		qe_setbrg(qe_port->us_info.rx_clock, baud, 16);