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>

1 files changed, 45 insertions, 0 deletions

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 75885d502749..507a25d692bb 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -280,6 +280,51 @@ 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
  *	@new_termios: desired new value