netdev - Re: [net-next-2.6 PATCH v2 3/3] fs_enet: add FEC TX buffer alignment workaround for MPC5121

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Date:	Wed, 17 Feb 2010 08:13:52 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Anatolij Gustschin <agust@...x.de>
Cc:	netdev@...r.kernel.org, linuxppc-dev@...abs.org,
	"David S. Miller" <davem@...emloft.net>,
	Detlev Zundel <dzu@...x.de>, Wolfgang Denk <wd@...x.de>,
	John Rigby <jcrigby@...il.com>,
	Piotr Ziecik <kosmo@...ihalf.com>
Subject: Re: [net-next-2.6 PATCH v2 3/3] fs_enet: add FEC TX buffer alignment 
	workaround for MPC5121

On Wed, Feb 17, 2010 at 7:55 AM, Anatolij Gustschin <agust@...x.de> wrote:
> MPC5121 FEC requeries 4-byte alignmnent for TX data buffers.
> This patch is a work around that copies misaligned tx packets
> to an aligned skb before sending.
>
> Signed-off-by: John Rigby <jcrigby@...il.com>
> Signed-off-by: Piotr Ziecik <kosmo@...ihalf.com>
> Signed-off-by: Wolfgang Denk <wd@...x.de>
> Signed-off-by: Anatolij Gustschin <agust@...x.de>

Acked-by: Grant Likely <grant.likely@...retlab.ca>

> ---
>  drivers/net/fs_enet/fs_enet-main.c |   44 ++++++++++++++++++++++++++++++++++++
>  1 files changed, 44 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/net/fs_enet/fs_enet-main.c b/drivers/net/fs_enet/fs_enet-main.c
> index 4297021..166a89d 100644
> --- a/drivers/net/fs_enet/fs_enet-main.c
> +++ b/drivers/net/fs_enet/fs_enet-main.c
> @@ -580,6 +580,37 @@ void fs_cleanup_bds(struct net_device *dev)
>
>  /**********************************************************************************/
>
> +#ifdef CONFIG_FS_ENET_MPC5121_FEC
> +/*
> + * MPC5121 FEC requeries 4-byte alignment for TX data buffer!
> + */
> +static struct sk_buff *tx_skb_align_workaround(struct net_device *dev,
> +                                              struct sk_buff *skb)
> +{
> +       struct sk_buff *new_skb;
> +       struct fs_enet_private *fep = netdev_priv(dev);
> +
> +       /* Alloc new skb */
> +       new_skb = dev_alloc_skb(ENET_RX_FRSIZE + 4);
> +       if (!new_skb) {
> +               dev_warn(fep->dev, "Memory squeeze, dropping tx packet.\n");
> +               return NULL;
> +       }
> +
> +       /* Make sure new skb is properly aligned */
> +       skb_align(new_skb, 4);
> +
> +       /* Copy data to new skb ... */
> +       skb_copy_from_linear_data(skb, new_skb->data, skb->len);
> +       skb_put(new_skb, skb->len);
> +
> +       /* ... and free an old one */
> +       dev_kfree_skb_any(skb);
> +
> +       return new_skb;
> +}
> +#endif
> +
>  static int fs_enet_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>        struct fs_enet_private *fep = netdev_priv(dev);
> @@ -588,6 +619,19 @@ static int fs_enet_start_xmit(struct sk_buff *skb, struct net_device *dev)
>        u16 sc;
>        unsigned long flags;
>
> +#ifdef CONFIG_FS_ENET_MPC5121_FEC
> +       if (((unsigned long)skb->data) & 0x3) {
> +               skb = tx_skb_align_workaround(dev, skb);
> +               if (!skb) {
> +                       /*
> +                        * We have lost packet due to memory allocation error
> +                        * in tx_skb_align_workaround(). Hopefully original
> +                        * skb is still valid, so try transmit it later.
> +                        */
> +                       return NETDEV_TX_BUSY;
> +               }
> +       }
> +#endif

Instead of
>        spin_lock_irqsave(&fep->tx_lock, flags);
>
>        /*
> --
> 1.6.3.3
>
>



-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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