USB: serial: add generic wait_until_sent implementation

Add generic wait_until_sent implementation which polls for empty
hardware buffers using the new port-operation tx_empty.

The generic implementation will be used for all sub-drivers that
implement tx_empty but does not define wait_until_sent.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 297665fdd16d..ba45170c78e5 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -253,6 +253,37 @@ int usb_serial_generic_chars_in_buffer(struct tty_struct *tty)
 }
 EXPORT_SYMBOL_GPL(usb_serial_generic_chars_in_buffer);
 
+void usb_serial_generic_wait_until_sent(struct tty_struct *tty, long timeout)
+{
+        struct usb_serial_port *port = tty->driver_data;
+        unsigned int bps;
+        unsigned long period;
+        unsigned long expire;
+
+        bps = tty_get_baud_rate(tty);
+        if (!bps)
+                bps = 9600;     /* B0 */
+        /*
+         * Use a poll-period of roughly the time it takes to send one
+         * character or at least one jiffy.
+         */
+        period = max_t(unsigned long, (10 * HZ / bps), 1);
+        period = min_t(unsigned long, period, timeout);
+
+        dev_dbg(&port->dev, "%s - timeout = %u ms, period = %u ms\n",
+                                        __func__, jiffies_to_msecs(timeout),
+                                        jiffies_to_msecs(period));
+        expire = jiffies + timeout;
+        while (!port->serial->type->tx_empty(port)) {
+                schedule_timeout_interruptible(period);
+                if (signal_pending(current))
+                        break;
+                if (time_after(jiffies, expire))
+                        break;
+        }
+}
+EXPORT_SYMBOL_GPL(usb_serial_generic_wait_until_sent);
+
 static int usb_serial_generic_submit_read_urb(struct usb_serial_port *port,
                                                 int index, gfp_t mem_flags)
 {