Date:	Fri, 18 Apr 2014 09:59:35 -0300
From:	Fabio Estevam <festevam@...il.com>
To:	Stanislav Meduna <stano@...una.org>
Cc:	Fabio Estevam <fabio.estevam@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Jim Baxter <jim_baxter@...tor.com>,
	Duan Fugang-B38611 <B38611@...escale.com>,
	Frank Li <Frank.Li@...escale.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: Freescale FEC i.MX28 restart problem

On Fri, Apr 18, 2014 at 8:46 AM, Stanislav Meduna <stano@...una.org> wrote:
> Hi,
>
> I am experiencing a problem with the ethernet controller on an
> i.MX28 SoC. When doing
>   /etc/init.d/networking restart
> sometimes I get "MDIO read timeout" and the controller does not
> recover. The problem is more prominent if the interface is communicating
> when the restart is performed.
>
> I have found that the reason is the EBERR bit being set somewher.
> The reference manual states:
>
>   Ethernet bus error. This bit indicates a system bus error occurs when a DMA
>   transaction is underway (Signal dma_eberr_int asserted). When the EBERR bit
>   is set, ETHER_EN is cleared, halting frame processing by the MAC. When this
>   occurs, software needs to insure proper actions (possibly resetting the
>   system) to resume normal operation.
>
> Clearing the ETHER_EN also disables the MII interrupts, so this
> explains why the controller does not recover.
>
> I assume the EBERR comes because of resetting the FEC at various
> places - the fec_restart is called from 7 and fec_stop from 5 places.
> It looks something here does not pay attention whether everything
> is idle. In addition to EBERR also the BABR and MII are set
> (MII because there was a MII transaction attempt, for babbling
> receiver I have no idea). In case it matters the PHY connected
> is the virtual port of the LAN9303 switch.
>
> Trying to put a graceful stop before the reset in fec_restart
> did not help. The controller is enabled when coming out of both
> paths involving the reset, it is after this it falls into the
> error state.
>
> My platform is 3.12.15-rt, but I assume the problem is not rt-related.
>
> The following patch remedies the situation, but this is just
> a demonstration and not a solution. The warning is sometimes
> output up to 3 times.
>
> Please Cc: me when replying.
>
>
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 1ec398b..cebb912 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -194,7 +194,7 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet MAC address");
>  #define FEC_ENET_MII   ((uint)0x00800000)      /* MII interrupt */
>  #define FEC_ENET_EBERR ((uint)0x00400000)      /* SDMA bus error */
>
> -#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF | FEC_ENET_MII)
> +#define FEC_DEFAULT_IMASK (FEC_ENET_TXF | FEC_ENET_RXF | FEC_ENET_MII | FEC_ENET_EBERR)
>  #define FEC_RX_DISABLED_IMASK (FEC_DEFAULT_IMASK & (~FEC_ENET_RXF))
>
>  /* The FEC stores dest/src/type/vlan, data, and checksum for receive packets.
> @@ -303,6 +303,31 @@ static void *swap_buffer(void *bufaddr, int len)
>         return bufaddr;
>  }
>
> +/* Re-enable the controller after an ethernet bus error.
> + *
> + * Reference manual: This bit indicates a system bus
> + * error occurs when a DMA transaction is underway
> + * (Signal dma_eberr_int asserted). When the EBERR bit
> + * is set, ETHER_EN is cleared, halting frame processing
> + * by the MAC. When this occurs, software needs to insure
> + * proper actions (possibly resetting the system) to resume
> + * normal operation.
> + *
> + * This seems to happen when we restart the controller.
> + */
> +static inline void fec_enet_clear_eberr_if_needed(struct net_device *ndev)
> +{
> +       struct fec_enet_private *fep = netdev_priv(ndev);
> +       u32 ctl = readl(fep->hwp + FEC_ECNTRL);
> +
> +       if (!(ctl & 2)) {
> +               ctl |= 2;
> +               writel(FEC_ENET_EBERR, fep->hwp + FEC_IEVENT);
> +               writel(ctl, fep->hwp + FEC_ECNTRL);
> +               netdev_warn(ndev, "Re-enabled after EBERR\n");
> +       }
> +}
> +
>  static int
>  fec_enet_clear_csum(struct sk_buff *skb, struct net_device *ndev)
>  {
> @@ -1059,6 +1084,10 @@ fec_enet_interrupt(int irq, void *dev_id)
>                         ret = IRQ_HANDLED;
>                         complete(&fep->mdio_done);
>                 }
> +
> +               if (int_events & FEC_ENET_EBERR)
> +                       fec_enet_clear_eberr_if_needed(ndev);
> +
>         } while (int_events);
>
>         return ret;
> @@ -1200,6 +1229,8 @@ static int fec_enet_mdio_read(struct mii_bus *bus, int mii_id, int regnum)
>         struct fec_enet_private *fep = bus->priv;
>         unsigned long time_left;
>
> +       fec_enet_clear_eberr_if_needed(fep->netdev);
> +
>         fep->mii_timeout = 0;
>         init_completion(&fep->mdio_done);
>
> @@ -1227,6 +1258,8 @@ static int fec_enet_mdio_write(struct mii_bus *bus, int mii_id, int regnum,
>         struct fec_enet_private *fep = bus->priv;
>         unsigned long time_left;
>
> +       fec_enet_clear_eberr_if_needed(fep->netdev);
> +
>         fep->mii_timeout = 0;
>         init_completion(&fep->mdio_done);

Could you try the latest Russell's FEC patches available at?
http://ftp.arm.linux.org.uk/cgit/linux-arm.git/log/?h=fec-testing

Regards,

Fabio Estevam
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