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

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@gmail.com>
Signed-off-by: Piotr Ziecik <kosmo@semihalf.com>
Signed-off-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
---
 drivers/net/fs_enet/fs_enet-main.c |   44 ++++++++++++++++++++++++++++++++++++
 1 files changed, 44 insertions(+), 0 deletions(-)

On Wed, Feb 17, 2010 at 7:55 AM, Anatolij Gustschin <agust@denx.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@gmail.com>
> Signed-off-by: Piotr Ziecik <kosmo@semihalf.com>
> Signed-off-by: Wolfgang Denk <wd@denx.de>
> Signed-off-by: Anatolij Gustschin <agust@denx.de>

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

Le mercredi 17 février 2010 à 15:55 +0100, Anatolij Gustschin a écrit :
> 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@gmail.com>
> Signed-off-by: Piotr Ziecik <kosmo@semihalf.com>
> Signed-off-by: Wolfgang Denk <wd@denx.de>
> Signed-off-by: Anatolij Gustschin <agust@denx.de>
> ---
>  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);


ENET_RX_FRSIZE looks strange in TX path

Why not using skb->len + 4 instead of ENET_RX_FRSIZE + 4 ?


> +	if (!new_skb) {
> +		dev_warn(fep->dev, "Memory squeeze, dropping tx packet.\n");

I am just wondering if this is ratelimited ?

> +		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.
> +			 */

Could you define 'try to transmit later' ?
Who is responsible to trigger this event ?


> +			return NETDEV_TX_BUSY;
> +		}
> +	}
> +#endif
>  	spin_lock_irqsave(&fep->tx_lock, flags);
>  
>  	/*


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On Wed, 17 Feb 2010 16:17:16 +0100
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Le mercredi 17 février 2010 à 15:55 +0100, Anatolij Gustschin a écrit :
...
> > +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);
> 
> 
> ENET_RX_FRSIZE looks strange in TX path
> 
> Why not using skb->len + 4 instead of ENET_RX_FRSIZE + 4 ?

I will fix it.

> > +	if (!new_skb) {
> > +		dev_warn(fep->dev, "Memory squeeze, dropping tx packet.\n");
> 
> I am just wondering if this is ratelimited ?

Right, it should be ratelimited, will fix it, too.

...
> >  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.
> > +			 */
> 
> Could you define 'try to transmit later' ?
> Who is responsible to trigger this event ?

The function returns NETDEV_TX_BUSY here, skb is not
consumed and will be requeued by sch_direct_xmit(), so
it is scheduled for resending later.

Thanks,
Anatolij
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