On Mon, 2016-10-24 at 14:18 +0100, Rafal Ozieblo wrote:
> New Cadence GEM hardware support Large Segment Offload (LSO):
> TCP segmentation offload (TSO) as well as UDP fragmentation
> offload (UFO). Support for those features was added to the driver.
>
> Signed-off-by: Rafal Ozieblo <raf...@cadence.com>
...
>
> +static int macb_lso_check_compatibility(struct sk_buff *skb, unsigned int
> hdrlen)
> +{
> + unsigned int nr_frags, f;
> +
> + if (skb_shinfo(skb)->gso_size == 0)
> + /* not LSO */
> + return -EPERM;
> +
> + /* there is only one buffer */
> + if (!skb_is_nonlinear(skb))
> + return 0;
> +
> + /* For LSO:
> + * When software supplies two or more payload buffers all payload
> buffers
> + * apart from the last must be a multiple of 8 bytes in size.
> + */
> + if (!IS_ALIGNED(skb_headlen(skb) - hdrlen, MACB_TX_LEN_ALIGN))
> + return -EPERM;
> +
> + nr_frags = skb_shinfo(skb)->nr_frags;
> + /* No need to check last fragment */
> + nr_frags--;
> + for (f = 0; f < nr_frags; f++) {
> + const skb_frag_t *frag = &skb_shinfo(skb)->frags[f];
> +
> + if (!IS_ALIGNED(skb_frag_size(frag), MACB_TX_LEN_ALIGN))
> + return -EPERM;
> + }
> + return 0;
> +}
> +
Very strange hardware requirements ;(
You should implement an .ndo_features_check method
to perform the checks from core networking stack, and not from your
ndo_start_xmit()
This has the huge advantage of not falling back to skb_linearize(skb)
which is very likely to fail with ~64 KB skbs anyway.
(Your ndo_features_check() would request software GSO instead ...)
