From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 24 Apr 2013 20:01:22 +0200
Subject: [PATCH] net/cpsw: use a lock around source testing
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/3.10/patches-3.10.4-rt1.tar.xz

For some reason on RT it happens that the TX interrupt fires over and
over again but according to tx_stat there is nothing going on. Same goes
for RX but not that often.
With this lock around it this is gone. However I still see from time to
time interrupts where each source is set to 0.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/net/ethernet/ti/cpsw.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Index: linux-stable/drivers/net/ethernet/ti/cpsw.c
===================================================================
--- linux-stable.orig/drivers/net/ethernet/ti/cpsw.c
+++ linux-stable/drivers/net/ethernet/ti/cpsw.c
@@ -490,7 +490,7 @@ void cpsw_rx_handler(void *token, int le
 		skb_put(skb, len);
 		cpts_rx_timestamp(priv->cpts, skb);
 		skb->protocol = eth_type_trans(skb, ndev);
-		netif_receive_skb(skb);
+		netif_rx(skb);
 		priv->stats.rx_bytes += len;
 		priv->stats.rx_packets++;
 	} else {
@@ -507,19 +507,24 @@ void cpsw_rx_handler(void *token, int le
 static irqreturn_t cpsw_interrupt(int irq, void *dev_id)
 {
 	struct cpsw_priv *priv = dev_id;
+	unsigned long flags;
 	u32 rx, tx, rx_thresh;
 
+	spin_lock_irqsave(&priv->lock, flags);
 	rx_thresh = __raw_readl(&priv->wr_regs->rx_thresh_stat);
 	rx = __raw_readl(&priv->wr_regs->rx_stat);
 	tx = __raw_readl(&priv->wr_regs->tx_stat);
-	if (!rx_thresh && !rx && !tx)
+	if (!rx_thresh && !rx && !tx) {
+		spin_unlock_irqrestore(&priv->lock, flags);
 		return IRQ_NONE;
+	}
 
 	cpsw_intr_disable(priv);
 	if (priv->irq_enabled == true) {
 		cpsw_disable_irq(priv);
 		priv->irq_enabled = false;
 	}
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 	if (netif_running(priv->ndev)) {
 		napi_schedule(&priv->napi);
@@ -541,7 +546,9 @@ static int cpsw_poll(struct napi_struct
 {
 	struct cpsw_priv	*priv = napi_to_priv(napi);
 	int			num_tx, num_rx;
+	unsigned long		flags;
 
+	spin_lock_irqsave(&priv->lock, flags);
 	num_tx = cpdma_chan_process(priv->txch, 128);
 	if (num_tx)
 		cpdma_ctlr_eoi(priv->dma, CPDMA_EOI_TX);