Hi,
I am writing n/w device driver for sdio wifi card. I am testing it on
embedded platform.
DMA controller on the platform is able to xfer data to sdio only if
source data buf address is 4 byte aligned.
The firmware on the card understands 802.3 frames with snap headers.
So, I convert it to the required format in my driver.
4 byte additional header is also attached to this frame and sent over sdio.
This all conversion effectively adds 12 byes to the frame received in
hard_xmit method.
Problem is, frame received in hard_xmit method is 2 byte aligned.
(skb->data is 2 byte aligned). As a result,
after addition of 12 bytes header, skb->data remains 2 byte aligned
instead of 4 byte aligned. And DMA controller refuses
to transfer it.
So, how can I request IP stack so that frame received in hard_xmit is
on 4 byte aligned boundry?
I believe setting NET_IP_ALIGN will only matter in rx path. is this correct?
Thanks in advance.
Regards,
Kalpesh
Kalpesh Rathod a ?crit :
> Hi,
>
> I am writing n/w device driver for sdio wifi card. I am testing it on
> embedded platform.
> DMA controller on the platform is able to xfer data to sdio only if
> source data buf address is 4 byte aligned.
>
> The firmware on the card understands 802.3 frames with snap headers.
> So, I convert it to the required format in my driver.
> 4 byte additional header is also attached to this frame and sent over sdio.
> This all conversion effectively adds 12 byes to the frame received in
> hard_xmit method.
>
> Problem is, frame received in hard_xmit method is 2 byte aligned.
> (skb->data is 2 byte aligned). As a result,
> after addition of 12 bytes header, skb->data remains 2 byte aligned
> instead of 4 byte aligned. And DMA controller refuses
> to transfer it.
>
> So, how can I request IP stack so that frame received in hard_xmit is
> on 4 byte aligned boundry?
You cannot.
Search for skb_copy_and_csum_dev() use in drivers.
drivers/net/via-rhine.c is a good example of a driver dealing with same
alignment requirement.
if ((rp->quirks & rqRhineI) &&
(((unsigned long)skb->data & 3) || skb_shinfo(skb)->nr_frags != 0 || skb->ip_summed == CHECKSUM_PARTIAL)) {
/* Must use alignment buffer. */
if (skb->len > PKT_BUF_SZ) {
/* packet too long, drop it */
dev_kfree_skb(skb);
rp->tx_skbuff[entry] = NULL;
dev->stats.tx_dropped++;
return NETDEV_TX_OK;
}
/* Padding is not copied and so must be redone. */
skb_copy_and_csum_dev(skb, rp->tx_buf[entry]);
if (skb->len < ETH_ZLEN)
memset(rp->tx_buf[entry] + skb->len, 0,
ETH_ZLEN - skb->len);
rp->tx_skbuff_dma[entry] = 0;
rp->tx_ring[entry].addr = cpu_to_le32(rp->tx_bufs_dma +
(rp->tx_buf[entry] -
rp->tx_bufs));
} else {
rp->tx_skbuff_dma[entry] =
pci_map_single(rp->pdev, skb->data, skb->len,
PCI_DMA_TODEVICE);
rp->tx_ring[entry].addr = cpu_to_le32(rp->tx_skbuff_dma[entry]);
}
On Thu, 23 Jul 2009 19:16:49 +0200
Eric Dumazet <[email protected]> wrote:
> Kalpesh Rathod a écrit :
> > Hi,
> >
> > I am writing n/w device driver for sdio wifi card. I am testing it on
> > embedded platform.
> > DMA controller on the platform is able to xfer data to sdio only if
> > source data buf address is 4 byte aligned.
> >
> > The firmware on the card understands 802.3 frames with snap headers.
> > So, I convert it to the required format in my driver.
> > 4 byte additional header is also attached to this frame and sent over sdio.
> > This all conversion effectively adds 12 byes to the frame received in
> > hard_xmit method.
> >
> > Problem is, frame received in hard_xmit method is 2 byte aligned.
> > (skb->data is 2 byte aligned). As a result,
> > after addition of 12 bytes header, skb->data remains 2 byte aligned
> > instead of 4 byte aligned. And DMA controller refuses
> > to transfer it.
> >
> > So, how can I request IP stack so that frame received in hard_xmit is
> > on 4 byte aligned boundry?
>
> You cannot.
>
> Search for skb_copy_and_csum_dev() use in drivers.
>
> drivers/net/via-rhine.c is a good example of a driver dealing with same
> alignment requirement.
>
> if ((rp->quirks & rqRhineI) &&
> (((unsigned long)skb->data & 3) || skb_shinfo(skb)->nr_frags != 0 || skb->ip_summed == CHECKSUM_PARTIAL)) {
There are wrappers for two of those tests
(!IS_ALIGNED(skb->data, 4) || skb_has_frags(skb) || skb->ip_summed == CHECKSUM_PARTIAL)