[PATCH v2] net: fec: Fix the disabling of RX interrupt

[Fabio Estevam <fabio.estevam@freescale.com>]

The correct way to disable FEC RX interrupt is to clean only the FEC_ENET_RXF 
bit.

Since commit dc975382d2e (net: fec: add napi support to improve proformance) 
FEC_RX_DISABLED_IMASK is being written to the FEC_IMASK register, which also 
incorrectly sets other bits as per the definitions below: 

#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF | FEC_ENET_MII)
#define FEC_RX_DISABLED_IMASK (FEC_DEFAULT_IMASK & (~FEC_ENET_RXF))

This fixes the following kernel crash:

Unable to handle kernel NULL pointer dereference at virtual address 00000002
pgd = 80004000
[00000002] *pgd=00000000
Internal error: Oops: 5 [#1] SMP ARM
Modules linked in:
CPU: 0    Not tainted  (3.8.0-rc7-next-20130218+ #1192)
PC is at fec_enet_interrupt+0xd0/0x354
LR is at fec_enet_interrupt+0xb8/0x354
pc : [<8034592c>]    lr : [<80345914>]    psr: 60000193

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
---
Changes since v1:
- Fix it also inside fec_enet_init and fix the kernel crash.

 drivers/net/ethernet/freescale/fec.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec.c b/drivers/net/ethernet/freescale/fec.c
index 0fe68c4..4eb0201 100644
--- a/drivers/net/ethernet/freescale/fec.c
+++ b/drivers/net/ethernet/freescale/fec.c
@@ -811,6 +811,7 @@ fec_enet_interrupt(int irq, void *dev_id)
 	struct fec_enet_private *fep = netdev_priv(ndev);
 	uint int_events;
 	irqreturn_t ret = IRQ_NONE;
+	int reg;
 
 	do {
 		int_events = readl(fep->hwp + FEC_IEVENT);
@@ -821,8 +822,9 @@ fec_enet_interrupt(int irq, void *dev_id)
 
 			/* Disable the RX interrupt */
 			if (napi_schedule_prep(&fep->napi)) {
-				writel(FEC_RX_DISABLED_IMASK,
-					fep->hwp + FEC_IMASK);
+				reg = readl(fep->hwp + FEC_IMASK);
+				reg &= ~FEC_ENET_RXF;
+				writel(reg, fep->hwp + FEC_IMASK);
 				__napi_schedule(&fep->napi);
 			}
 		}
@@ -1598,7 +1600,7 @@ static int fec_enet_init(struct net_device *ndev)
 	struct fec_enet_private *fep = netdev_priv(ndev);
 	struct bufdesc *cbd_base;
 	struct bufdesc *bdp;
-	int i;
+	int i, reg;
 
 	/* Allocate memory for buffer descriptors. */
 	cbd_base = dma_alloc_coherent(NULL, PAGE_SIZE, &fep->bd_dma,
@@ -1628,7 +1630,10 @@ static int fec_enet_init(struct net_device *ndev)
 	ndev->netdev_ops = &fec_netdev_ops;
 	ndev->ethtool_ops = &fec_enet_ethtool_ops;
 
-	writel(FEC_RX_DISABLED_IMASK, fep->hwp + FEC_IMASK);
+	reg = readl(fep->hwp + FEC_IMASK);
+	reg &= ~FEC_ENET_RXF;
+	writel(reg, fep->hwp + FEC_IMASK);
+
 	netif_napi_add(ndev, &fep->napi, fec_enet_rx_napi, FEC_NAPI_WEIGHT);
 
 	/* Initialize the receive buffer descriptors. */
-- 
1.7.9.5