serial: txx9: Don't allow CS5-6

stable inclusion
from stable-v5.10.122
commit 00456b932e16289de09508a570c6a6dcb0b1ebaf
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5W6OE

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=00456b932e16289de09508a570c6a6dcb0b1ebaf

--------------------------------

[ Upstream commit 79ac8865 ]

Only CS7 and CS8 are supported but CSIZE is not sanitized with
CS5 or CS6 to CS8.

Set CSIZE correctly so that userspace knows the effective value.
Incorrect CSIZE also results in miscalculation of the frame bits in
tty_get_char_size() or in its predecessor where the roughly the same
code is directly within uart_update_timeout().

Fixes: 1da177e4 (Linux-2.6.12-rc2)
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220519081808.3776-5-ilpo.jarvinen@linux.intel.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

drivers/tty/serial/serial_txx9.c

@@ -644,6 +644,8 @@ serial_txx9_set_termios(struct uart_port *port, struct ktermios *termios,
 	case CS6:	/* not supported */
 	case CS8:
 		cval |= TXX9_SILCR_UMODE_8BIT;
+		termios->c_cflag &= ~CSIZE;
+		termios->c_cflag |= CS8;
 		break;
 	}