USB: serial: ftdi_sio: fix setting latency for unprivileged users

commit bb246681b3ed0967489a7401ad528c1aaa1a4c2e upstream.

Commit 557aaa7ffab6 ("ft232: support the ASYNC_LOW_LATENCY
flag") enables unprivileged users to set the FTDI latency timer,
but there was a logic flaw that skipped sending the corresponding
USB control message to the device.

Specifically, the device latency timer would not be updated until next
open, something which was later also inadvertently broken by commit
c19db4c9e49a ("USB: ftdi_sio: set device latency timeout at port
probe").

A recent commit c6dce2626606 ("USB: serial: ftdi_sio: fix extreme
low-latency setting") disabled the low-latency mode by default so we now
need this fix to allow unprivileged users to again enable it.

Signed-off-by: Anthony Mallet <anthony.mallet@laas.fr>
[johan: amend commit message]
Fixes: 557aaa7ffab6 ("ft232: support the ASYNC_LOW_LATENCY flag")
Fixes: c19db4c9e49a ("USB: ftdi_sio: set device latency timeout at port probe").
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 7ce28ef191e3b052028fb2ffeb39d2db1eb0ddfa..a7638bbde315c32d58cfb3e46390cb113c813bc6 100644 (file)
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1506,9 +1506,9 @@ static int set_serial_info(struct tty_struct *tty,
                                        (new_serial.flags & ASYNC_FLAGS));
        priv->custom_divisor = new_serial.custom_divisor;
 
+check_and_exit:
        write_latency_timer(port);
 
-check_and_exit:
        if ((old_priv.flags & ASYNC_SPD_MASK) !=
             (priv->flags & ASYNC_SPD_MASK)) {
                if ((priv->flags & ASYNC_SPD_MASK) == ASYNC_SPD_HI)