use mutex instead of semaphore in RocketPort driver v3

index 76357c8..af9379b 100644
@@ -702,7 +702,7 @@ static void init_r_port(int board, int aiop, int chan, struct pci_dev *pci_dev)
 		}
 	}
 	spin_lock_init(&info->slock);
-	sema_init(&info->write_sem, 1);
+	mutex_init(&info->write_mtx);
 	rp_table[line] = info;
 	if (pci_dev)
 		tty_register_device(rocket_driver, line, &pci_dev->dev);

@@ -1662,7 +1662,7 @@ static void rp_put_char(struct tty_struct *tty, unsigned char ch)
 		return;
 
 	/*  Grab the port write semaphore, locking out other processes that try to write to this port */
-	down(&info->write_sem);
+	mutex_lock(&info->write_mtx);
 
 #ifdef ROCKET_DEBUG_WRITE
 	printk(KERN_INFO "rp_put_char %c...", ch);

@@ -1684,7 +1684,7 @@ static void rp_put_char(struct tty_struct *tty, unsigned char ch)
 		info->xmit_fifo_room--;
 	}
 	spin_unlock_irqrestore(&info->slock, flags);
-	up(&info->write_sem);
+	mutex_unlock(&info->write_mtx);
 }
 
 /*

@@ -1706,7 +1706,8 @@ static int rp_write(struct tty_struct *tty,
 	if (count <= 0 || rocket_paranoia_check(info, "rp_write"))
 		return 0;
 
-	down_interruptible(&info->write_sem);
+	if (mutex_lock_interruptible(&info->write_mtx))
+		return -ERESTARTSYS;
 
 #ifdef ROCKET_DEBUG_WRITE
 	printk(KERN_INFO "rp_write %d chars...", count);

@@ -1777,7 +1778,7 @@ end:
 		wake_up_interruptible(&tty->poll_wait);
 #endif
 	}
-	up(&info->write_sem);
+	mutex_unlock(&info->write_mtx);
 	return retval;
 }
 

index 3a8bcc8..04bcf61 100644
@@ -1171,7 +1171,7 @@ struct r_port {
 	struct wait_queue *close_wait;
 #endif
 	spinlock_t slock;
-	struct semaphore write_sem;
+	struct mutex write_mtx;
 };
 
 #define RPORT_MAGIC 0x525001