net/sonic: Clear interrupt flags immediately

The chip can change a packet's descriptor status flags at any time.
However, an active interrupt flag gets cleared rather late. This
allows a race condition that could theoretically lose an interrupt.
Fix this by clearing asserted interrupt flags immediately.

Fixes: efcce839 ("[PATCH] macsonic/jazzsonic network drivers update")
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/natsemi/sonic.c

@@ -304,10 +304,11 @@ static irqreturn_t sonic_interrupt(int irq, void *dev_id)
 	}
 
 	do {
+		SONIC_WRITE(SONIC_ISR, status); /* clear the interrupt(s) */
+
 		if (status & SONIC_INT_PKTRX) {
 			netif_dbg(lp, intr, dev, "%s: packet rx\n", __func__);
 			sonic_rx(dev);	/* got packet(s) */
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_PKTRX); /* clear the interrupt */
 		}
 
 		if (status & SONIC_INT_TXDN) {
@@ -362,7 +363,6 @@ static irqreturn_t sonic_interrupt(int irq, void *dev_id)
 			if (freed_some || lp->tx_skb[entry] == NULL)
 				netif_wake_queue(dev);  /* The ring is no longer full */
 			lp->cur_tx = entry;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_TXDN); /* clear the interrupt */
 		}
 
 		/*
@@ -372,42 +372,31 @@ static irqreturn_t sonic_interrupt(int irq, void *dev_id)
 			netif_dbg(lp, rx_err, dev, "%s: rx fifo overrun\n",
 				  __func__);
 			lp->stats.rx_fifo_errors++;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_RFO); /* clear the interrupt */
 		}
 		if (status & SONIC_INT_RDE) {
 			netif_dbg(lp, rx_err, dev, "%s: rx descriptors exhausted\n",
 				  __func__);
 			lp->stats.rx_dropped++;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_RDE); /* clear the interrupt */
 		}
 		if (status & SONIC_INT_RBAE) {
 			netif_dbg(lp, rx_err, dev, "%s: rx buffer area exceeded\n",
 				  __func__);
 			lp->stats.rx_dropped++;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_RBAE); /* clear the interrupt */
 		}
 
 		/* counter overruns; all counters are 16bit wide */
-		if (status & SONIC_INT_FAE) {
+		if (status & SONIC_INT_FAE)
 			lp->stats.rx_frame_errors += 65536;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_FAE); /* clear the interrupt */
-		}
-		if (status & SONIC_INT_CRC) {
+		if (status & SONIC_INT_CRC)
 			lp->stats.rx_crc_errors += 65536;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_CRC); /* clear the interrupt */
-		}
-		if (status & SONIC_INT_MP) {
+		if (status & SONIC_INT_MP)
 			lp->stats.rx_missed_errors += 65536;
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_MP); /* clear the interrupt */
-		}
 
 		/* transmit error */
-		if (status & SONIC_INT_TXER) {
+		if (status & SONIC_INT_TXER)
 			if (SONIC_READ(SONIC_TCR) & SONIC_TCR_FU)
 				netif_dbg(lp, tx_err, dev, "%s: tx fifo underrun\n",
 					  __func__);
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_TXER); /* clear the interrupt */
-		}
 
 		/* bus retry */
 		if (status & SONIC_INT_BR) {
@@ -416,13 +405,8 @@ static irqreturn_t sonic_interrupt(int irq, void *dev_id)
 			/* ... to help debug DMA problems causing endless interrupts. */
 			/* Bounce the eth interface to turn on the interrupt again. */
 			SONIC_WRITE(SONIC_IMR, 0);
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_BR); /* clear the interrupt */
 		}
 
-		/* load CAM done */
-		if (status & SONIC_INT_LCD)
-			SONIC_WRITE(SONIC_ISR, SONIC_INT_LCD); /* clear the interrupt */
-
 		status = SONIC_READ(SONIC_ISR) & SONIC_IMR_DEFAULT;
 	} while (status);