[patch 3/5] [PREEMPT_RT] Changing interrupt handlers from running in thread to hardirq and back runtime.

[Esben Nielsen <nielsen.esben@googlemail.com>]

Makes it possible for the e100 ethernet driver to have it's interrupt handler
in both hard-irq and threaded context under PREEMPT_RT.

Index: linux-2.6.16-rt23.spin_mutex/drivers/net/e100.c
===================================================================
--- linux-2.6.16-rt23.spin_mutex.orig/drivers/net/e100.c
+++ linux-2.6.16-rt23.spin_mutex/drivers/net/e100.c
@@ -530,7 +530,7 @@ struct nic {
  	enum ru_state ru_running;

  	spinlock_t cb_lock			____cacheline_aligned;
-	spinlock_t cmd_lock;
+	spin_mutex_t cmd_lock;
  	struct csr __iomem *csr;
  	enum scb_cmd_lo cuc_cmd;
  	unsigned int cbs_avail;
@@ -1950,6 +1950,30 @@ static int e100_rx_alloc_list(struct nic
  	return 0;
  }

+static int e100_change_context(int irq, void *dev_id,
+			       enum change_context_cmd cmd)
+{
+	struct net_device *netdev = dev_id;
+	struct nic *nic = netdev_priv(netdev);
+
+	switch(cmd)
+	{
+	case IRQ_TO_HARDIRQ:
+		if(!spin_mutexes_can_spin())
+			return -ENOSYS;
+
+		spin_mutex_to_spin(&nic->cmd_lock);
+		break;
+	case IRQ_CAN_THREAD:
+		/* Ok - return 0 */
+		break;
+	case IRQ_TO_THREADED:
+		spin_mutex_to_mutex(&nic->cmd_lock);
+		break;
+	}
+	return 0; /* Ok */
+}
+
  static irqreturn_t e100_intr(int irq, void *dev_id, struct pt_regs *regs)
  {
  	struct net_device *netdev = dev_id;
@@ -2064,9 +2088,12 @@ static int e100_up(struct nic *nic)
  	e100_set_multicast_list(nic->netdev);
  	e100_start_receiver(nic, NULL);
  	mod_timer(&nic->watchdog, jiffies);
-	if((err = request_irq(nic->pdev->irq, e100_intr, SA_SHIRQ,
-		nic->netdev->name, nic->netdev)))
+	if((err = request_irq2(nic->pdev->irq, e100_intr,
+			       SA_SHIRQ|SA_MUST_THREAD_RT,
+			       nic->netdev->name, nic->netdev,
+			       e100_change_context)))
  		goto err_no_irq;
+
  	netif_wake_queue(nic->netdev);
  	netif_poll_enable(nic->netdev);
  	/* enable ints _after_ enabling poll, preventing a race between

--