USB: usb_debug, usb_generic_serial: implement multi urb write

The usb_debug driver, when used as the console, will always fail to
insert the carriage return and new line sequence as well as randomly
drop console output.  This is a result of only having the single
write_urb and that the tty layer will have a lock that prevents the
processing of the back to back urb requests.

The solution is to allow more than one urb to be outstanding and have
a slightly deeper transmit queue.  The idea and some code is borrowed
from the ftdi_sio usb driver.

The generic usb serial driver was modified so as to allow the classic
method of 1 write urb, or a multi write urb scheme with N allowed
outstanding urbs where N is controlled by max_in_flight_urbs.  When
max_in_flight_urbs in a "struct usb_serial_driver" is non zero the
multi write urb scheme will be used.

The size of 4000 was selected for the usb_debug driver so that the
driver lowers possibility of losing the queued console messages during
the kernel startup.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 116 insertions, 7 deletions

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index be82ea95672..c919686521f 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -190,6 +190,88 @@ void usb_serial_generic_close(struct usb_serial_port *port)
         generic_cleanup(port);
 }
 
+static int usb_serial_multi_urb_write(struct tty_struct *tty,
+        struct usb_serial_port *port, const unsigned char *buf, int count)
+{
+        unsigned long flags;
+        struct urb *urb;
+        unsigned char *buffer;
+        int status;
+        int towrite;
+        int bwrite = 0;
+
+        dbg("%s - port %d", __func__, port->number);
+
+        if (count == 0)
+                dbg("%s - write request of 0 bytes", __func__);
+
+        while (count > 0) {
+                towrite = (count > port->bulk_out_size) ?
+                        port->bulk_out_size : count;
+                spin_lock_irqsave(&port->lock, flags);
+                if (port->urbs_in_flight >
+                    port->serial->type->max_in_flight_urbs) {
+                        spin_unlock_irqrestore(&port->lock, flags);
+                        dbg("%s - write limit hit\n", __func__);
+                        return bwrite;
+                }
+                port->tx_bytes_flight += towrite;
+                port->urbs_in_flight++;
+                spin_unlock_irqrestore(&port->lock, flags);
+
+                buffer = kmalloc(towrite, GFP_ATOMIC);
+                if (!buffer) {
+                        dev_err(&port->dev,
+                        "%s ran out of kernel memory for urb ...\n", __func__);
+                        goto error_no_buffer;
+                }
+
+                urb = usb_alloc_urb(0, GFP_ATOMIC);
+                if (!urb) {
+                        dev_err(&port->dev, "%s - no more free urbs\n",
+                                __func__);
+                        goto error_no_urb;
+                }
+
+                /* Copy data */
+                memcpy(buffer, buf + bwrite, towrite);
+                usb_serial_debug_data(debug, &port->dev, __func__,
+                                      towrite, buffer);
+                /* fill the buffer and send it */
+                usb_fill_bulk_urb(urb, port->serial->dev,
+                        usb_sndbulkpipe(port->serial->dev,
+                                        port->bulk_out_endpointAddress),
+                        buffer, towrite,
+                        usb_serial_generic_write_bulk_callback, port);
+
+                status = usb_submit_urb(urb, GFP_ATOMIC);
+                if (status) {
+                        dev_err(&port->dev,
+                                "%s - failed submitting write urb, error %d\n",
+                                __func__, status);
+                        goto error;
+                }
+
+                /* This urb is the responsibility of the host driver now */
+                usb_free_urb(urb);
+                dbg("%s write: %d", __func__, towrite);
+                count -= towrite;
+                bwrite += towrite;
+        }
+        return bwrite;
+
+error:
+        usb_free_urb(urb);
+error_no_urb:
+        kfree(buffer);
+error_no_buffer:
+        spin_lock_irqsave(&port->lock, flags);
+        port->urbs_in_flight--;
+        port->tx_bytes_flight -= towrite;
+        spin_unlock_irqrestore(&port->lock, flags);
+        return bwrite;
+}
+
 int usb_serial_generic_write(struct tty_struct *tty,
         struct usb_serial_port *port, const unsigned char *buf, int count)
 {
@@ -207,6 +289,11 @@ int usb_serial_generic_write(struct tty_struct *tty,
         /* only do something if we have a bulk out endpoint */
         if (serial->num_bulk_out) {
                 unsigned long flags;
+
+                if (serial->type->max_in_flight_urbs)
+                        return usb_serial_multi_urb_write(tty, port,
+                                                          buf, count);
+
                 spin_lock_irqsave(&port->lock, flags);
                 if (port->write_urb_busy) {
                         spin_unlock_irqrestore(&port->lock, flags);
@@ -257,15 +344,18 @@ int usb_serial_generic_write_room(struct tty_struct *tty)
 {
         struct usb_serial_port *port = tty->driver_data;
         struct usb_serial *serial = port->serial;
+        unsigned long flags;
         int room = 0;
 
         dbg("%s - port %d", __func__, port->number);
-
-        /* FIXME: Locking */
-        if (serial->num_bulk_out) {
-                if (!(port->write_urb_busy))
+        spin_lock_irqsave(&port->lock, flags);
+        if (serial->type->max_in_flight_urbs) {
+                if (port->urbs_in_flight < serial->type->max_in_flight_urbs)
                         room = port->bulk_out_size;
+        } else if (serial->num_bulk_out && !(port->write_urb_busy)) {
+                room = port->bulk_out_size;
         }
+        spin_unlock_irqrestore(&port->lock, flags);
 
         dbg("%s - returns %d", __func__, room);
         return room;
@@ -276,11 +366,16 @@ int usb_serial_generic_chars_in_buffer(struct tty_struct *tty)
         struct usb_serial_port *port = tty->driver_data;
         struct usb_serial *serial = port->serial;
         int chars = 0;
+        unsigned long flags;
 
         dbg("%s - port %d", __func__, port->number);
 
-        /* FIXME: Locking */
-        if (serial->num_bulk_out) {
+        if (serial->type->max_in_flight_urbs) {
+                spin_lock_irqsave(&port->lock, flags);
+                chars = port->tx_bytes_flight;
+                spin_unlock_irqrestore(&port->lock, flags);
+        } else if (serial->num_bulk_out) {
+                /* FIXME: Locking */
                 if (port->write_urb_busy)
                         chars = port->write_urb->transfer_buffer_length;
         }
@@ -363,12 +458,24 @@ EXPORT_SYMBOL_GPL(usb_serial_generic_read_bulk_callback);
 
 void usb_serial_generic_write_bulk_callback(struct urb *urb)
 {
+        unsigned long flags;
         struct usb_serial_port *port = urb->context;
         int status = urb->status;
 
         dbg("%s - port %d", __func__, port->number);
 
-        port->write_urb_busy = 0;
+        if (port->serial->type->max_in_flight_urbs) {
+                spin_lock_irqsave(&port->lock, flags);
+                --port->urbs_in_flight;
+                port->tx_bytes_flight -= urb->transfer_buffer_length;
+                if (port->urbs_in_flight < 0)
+                        port->urbs_in_flight = 0;
+                spin_unlock_irqrestore(&port->lock, flags);
+        } else {
+                /* Handle the case for single urb mode */
+                port->write_urb_busy = 0;
+        }
+
         if (status) {
                 dbg("%s - nonzero write bulk status received: %d",
                     __func__, status);
diff --git a/drivers/usb/serial/usb_debug.c b/drivers/usb/serial/usb_debug.c
index 6c9cbb59552..a9427a8b867 100644
--- a/drivers/usb/serial/usb_debug.c
+++ b/drivers/usb/serial/usb_debug.c
@@ -15,6 +15,7 @@
 #include <linux/usb.h>
 #include <linux/usb/serial.h>
 
+#define URB_DEBUG_MAX_IN_FLIGHT_URBS    4000
 #define USB_DEBUG_MAX_PACKET_SIZE       8
 
 static struct usb_device_id id_table [] = {
@@ -46,6 +47,7 @@ static struct usb_serial_driver debug_device = {
         .id_table =             id_table,
         .num_ports =            1,
         .open =                 usb_debug_open,
+        .max_in_flight_urbs =   URB_DEBUG_MAX_IN_FLIGHT_URBS,
 };
 
 static int __init debug_init(void)