staging: fwserial: fix TIOCGSERIAL implementation

stable inclusion
from stable-5.10.37
commit 2c3ce3d84e80a4adcabed21b299058ff0b184212
bugzilla: 51868
CVE: NA

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

[ Upstream commit 5e84a66f ]

TIOCSSERIAL is a horrid, underspecified, legacy interface which for most
serial devices is only useful for setting the close_delay and
closing_wait parameters.

The xmit_fifo_size parameter could be used to set the hardware transmit
fifo size of a legacy UART when it could not be detected, but the
interface is limited to eight bits and should be left unset when not
used.

Fix the fwserial implementation by dropping its custom interpretation of
the unused xmit_fifo_size field, which was overflowed with the driver
FIFO size. Also leave the type and flags fields unset as these cannot be
changed.

The close_delay and closing_wait parameters returned by TIOCGSERIAL are
specified in centiseconds. The driver does not yet support changing
closing_wait, but let's report back the default value actually used (30
seconds).

Fixes: 7355ba34 ("staging: fwserial: Add TTY-over-Firewire serial driver")
Signed-off-by: NJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210407102334.32361-5-johan@kernel.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/staging/fwserial/fwserial.c

@@ -1218,13 +1218,12 @@ static int get_serial_info(struct tty_struct *tty,
 	struct fwtty_port *port = tty->driver_data;
 
 	mutex_lock(&port->port.mutex);
-	ss->type =  PORT_UNKNOWN;
-	ss->line =  port->port.tty->index;
-	ss->flags = port->port.flags;
-	ss->xmit_fifo_size = FWTTY_PORT_TXFIFO_LEN;
+	ss->line = port->index;
 	ss->baud_base = 400000000;
 	ss->close_delay = jiffies_to_msecs(port->port.close_delay) / 10;
+	ss->closing_wait = 3000;
 	mutex_unlock(&port->port.mutex);
+
 	return 0;
 }