tty: make tty_get_{char,frame}_size available

Many tty drivers contain code to compute bits count depending on termios
cflags. So extract this code from serial core to two separate tty helper
functions:
* tty_get_char_size -- only size of a character, without flags,
* tty_get_frame_size -- complete size of a frame including flags.

In the next patch, calls to these new functions replace many copies of
this code.

Note that we accept only cflag as a parameter. That's because some
callers like pch_uart_startup or sunsab_console_setup don't have at hand
termios which we could pass around.

Cc: Joe Perches <joe@perches.com>
Cc: Johan Hovold <johan@kernel.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210610090247.2593-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -334,39 +334,15 @@ void
 uart_update_timeout(struct uart_port *port, unsigned int cflag,
 		    unsigned int baud)
 {
-	unsigned int bits;
+	unsigned int size;
 
-	/* byte size and parity */
-	switch (cflag & CSIZE) {
-	case CS5:
-		bits = 7;
-		break;
-	case CS6:
-		bits = 8;
-		break;
-	case CS7:
-		bits = 9;
-		break;
-	default:
-		bits = 10;
-		break; /* CS8 */
-	}
-
-	if (cflag & CSTOPB)
-		bits++;
-	if (cflag & PARENB)
-		bits++;
-
-	/*
-	 * The total number of bits to be transmitted in the fifo.
-	 */
-	bits = bits * port->fifosize;
+	size = tty_get_frame_size(cflag) * port->fifosize;
 
 	/*
 	 * Figure the timeout to send the above number of bits.
 	 * Add .02 seconds of slop
 	 */
-	port->timeout = (HZ * bits) / baud + HZ/50;
+	port->timeout = (HZ * size) / baud + HZ/50;
 }
 
 EXPORT_SYMBOL(uart_update_timeout);

drivers/tty/tty_ioctl.c

@@ -279,6 +279,51 @@ int tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b)
 }
 EXPORT_SYMBOL(tty_termios_hw_change);
 
+/**
+ *	tty_get_char_size	-	get size of a character
+ *	@cflag: termios cflag value
+ *
+ *	Get the size (in bits) of a character depending on @cflag's %CSIZE
+ *	setting.
+ */
+unsigned char tty_get_char_size(unsigned int cflag)
+{
+	switch (cflag & CSIZE) {
+	case CS5:
+		return 5;
+	case CS6:
+		return 6;
+	case CS7:
+		return 7;
+	case CS8:
+	default:
+		return 8;
+	}
+}
+EXPORT_SYMBOL_GPL(tty_get_char_size);
+
+/**
+ *	tty_get_frame_size	-	get size of a frame
+ *	@cflag: termios cflag value
+ *
+ *	Get the size (in bits) of a frame depending on @cflag's %CSIZE, %CSTOPB,
+ *	and %PARENB setting. The result is a sum of character size, start and
+ *	stop bits -- one bit each -- second stop bit (if set), and parity bit
+ *	(if set).
+ */
+unsigned char tty_get_frame_size(unsigned int cflag)
+{
+	unsigned char bits = 2 + tty_get_char_size(cflag);
+
+	if (cflag & CSTOPB)
+		bits++;
+	if (cflag & PARENB)
+		bits++;
+
+	return bits;
+}
+EXPORT_SYMBOL_GPL(tty_get_frame_size);
+
 /**
  *	tty_set_termios		-	update termios values
  *	@tty: tty to update

include/linux/tty.h

@@ -495,6 +495,9 @@ static inline speed_t tty_get_baud_rate(struct tty_struct *tty)
 	return tty_termios_baud_rate(&tty->termios);
 }
 
+unsigned char tty_get_char_size(unsigned int cflag);
+unsigned char tty_get_frame_size(unsigned int cflag);
+
 extern void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old);
 extern int tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b);
 extern int tty_set_termios(struct tty_struct *tty, struct ktermios *kt);