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

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(-)

2013/2/19 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);


This is not correct fix.
Read, OR and write is not atomic. Need lock.
But if use hw_lock, it cause dead lock.
I spend some time to remove such lock.

Can you tell which bit cause crash?

>                                 __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
>
>
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