On Wed, Feb 17, 2021 at 12:55:42AM +0100, Linus Walleij wrote:
> Support also transmitting frames using the custom "8899 A"
> 4 byte tag.
>
> Qingfang came up with the solution: we need to pad the
> ethernet frame to 60 bytes using eth_skb_pad(), then the
> switch will happily accept frames with custom tags.
I think it's pretty frustrating to realize that 'it didn't werk' because
you only tested with ping.
> Cc: Mauri Sandberg <sandb...@mailfence.com>
> Reported-by: DENG Qingfang <dqf...@gmail.com>
Reported-by seems like a bit of an understatement. Suggested-by maybe?
> Fixes: efd7fe68f0c6 ("net: dsa: tag_rtl4_a: Implement Realtek 4 byte A tag")
> Signed-off-by: Linus Walleij <linus.wall...@linaro.org>
> ---
> net/dsa/tag_rtl4_a.c | 43 +++++++++++++++++++++++++++++--------------
> 1 file changed, 29 insertions(+), 14 deletions(-)
>
> diff --git a/net/dsa/tag_rtl4_a.c b/net/dsa/tag_rtl4_a.c
> index 2646abe5a69e..c17d39b4a1a0 100644
> --- a/net/dsa/tag_rtl4_a.c
> +++ b/net/dsa/tag_rtl4_a.c
> @@ -12,9 +12,7 @@
> *
> * The 2 bytes tag form a 16 bit big endian word. The exact
> * meaning has been guessed from packet dumps from ingress
> - * frames, as no working egress traffic has been available
> - * we do not know the format of the egress tags or if they
> - * are even supported.
> + * frames.
> */
>
> #include <linux/etherdevice.h>
> @@ -36,17 +34,34 @@
> static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
> struct net_device *dev)
> {
> - /*
> - * Just let it pass thru, we don't know if it is possible
> - * to tag a frame with the 0x8899 ethertype and direct it
> - * to a specific port, all attempts at reverse-engineering have
> - * ended up with the frames getting dropped.
> - *
> - * The VLAN set-up needs to restrict the frames to the right port.
> - *
> - * If you have documentation on the tagging format for RTL8366RB
> - * (tag type A) then please contribute.
> - */
> + struct dsa_port *dp = dsa_slave_to_port(dev);
> + u8 *tag;
> + u16 *p;
> + u16 out;
> +
> + /* Pad out to at least 60 bytes */
> + if (unlikely(eth_skb_pad(skb)))
> + return NULL;
> + if (skb_cow_head(skb, RTL4_A_HDR_LEN) < 0)
> + return NULL;
> +
> + netdev_dbg(dev, "add realtek tag to package to port %d\n",
> + dp->index);
You should probably remove any sort of printing from the hot path.
> + skb_push(skb, RTL4_A_HDR_LEN);
> +
> + memmove(skb->data, skb->data + RTL4_A_HDR_LEN, 2 * ETH_ALEN);
> + tag = skb->data + 2 * ETH_ALEN;
> +
> + /* Set Ethertype */
> + p = (u16 *)tag;
> + *p = htons(RTL4_A_ETHERTYPE);
> +
> + out = (RTL4_A_PROTOCOL_RTL8366RB << 12) | (2 << 8);
> + /* The lower bits is the port numer */
> + out |= (u8)dp->index;
> + p = (u16 *)(tag + 2);
> + *p = htons(out);
> +
> return skb;
> }
>
> --
> 2.29.2
>
