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USB: serial: keyspan_pda: fix write unthrottling 

The driver did not update its view of the available device buffer space
until write() was called in task context. This meant that write_room()
would return 0 even after the device had sent a write-unthrottle
notification, something which could lead to blocked writers not being
woken up (e.g. when using OPOST).

Note that we must also request an unthrottle notification is case a
write() request fills the device buffer exactly.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
This commit is contained in:
Johan Hovold 2020-10-25 18:45:52 +01:00
parent 49fbb8e37a
commit 320f9028c7
1 changed files with 20 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
drivers/usb/serial/keyspan_pda.c
View File

@ -40,6 +40,8 @@
#define DRIVER_AUTHOR "Brian Warner <warner@lothar.com>"
#define DRIVER_DESC "USB Keyspan PDA Converter driver"
#define KEYSPAN_TX_THRESHOLD 16
struct keyspan_pda_private {
int tx_room;
int tx_throttled;
@ -110,7 +112,7 @@ static void keyspan_pda_request_unthrottle(struct work_struct *work)
7, /* request_unthrottle */
USB_TYPE_VENDOR | USB_RECIP_INTERFACE
| USB_DIR_OUT,
16, /* value: threshold */
KEYSPAN_TX_THRESHOLD,
0, /* index */
NULL,
0,
@ -129,6 +131,8 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
int retval;
int status = urb->status;
struct keyspan_pda_private *priv;
unsigned long flags;
priv = usb_get_serial_port_data(port);
switch (status) {
@ -171,7 +175,10 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
case 1: /* modemline change */
break;
case 2: /* tx unthrottle interrupt */
spin_lock_irqsave(&port->lock, flags);
priv->tx_throttled = 0;
priv->tx_room = max(priv->tx_room, KEYSPAN_TX_THRESHOLD);
spin_unlock_irqrestore(&port->lock, flags);
/* queue up a wakeup at scheduler time */
usb_serial_port_softint(port);
break;
@ -505,7 +512,8 @@ static int keyspan_pda_write(struct tty_struct *tty,
goto exit;
}
}
if (count > priv->tx_room) {
if (count >= priv->tx_room) {
/* we're about to completely fill the Tx buffer, so
we'll be throttled afterwards. */
count = priv->tx_room;
@ -560,14 +568,17 @@ static void keyspan_pda_write_bulk_callback(struct urb *urb)
static int keyspan_pda_write_room(struct tty_struct *tty)
{
struct usb_serial_port *port = tty->driver_data;
struct keyspan_pda_private *priv;
priv = usb_get_serial_port_data(port);
/* used by n_tty.c for processing of tabs and such. Giving it our
conservative guess is probably good enough, but needs testing by
running a console through the device. */
return priv->tx_room;
}
struct keyspan_pda_private *priv = usb_get_serial_port_data(port);
unsigned long flags;
int room = 0;
spin_lock_irqsave(&port->lock, flags);
if (test_bit(0, &port->write_urbs_free) && !priv->tx_throttled)
room = priv->tx_room;
spin_unlock_irqrestore(&port->lock, flags);
return room;
}
static int keyspan_pda_chars_in_buffer(struct tty_struct *tty)
{