Re: [PATCH net-next v4 1/3] dsa: add support for Arrow XRS700x tag trailer

[Vladimir Oltean <olteanv@gmail.com>]

On Wed, Jan 13, 2021 at 08:59:20AM -0600, George McCollister wrote:
> Add support for Arrow SpeedChips XRS700x single byte tag trailer. This
> is modeled on tag_trailer.c which works in a similar way.
> 
> Signed-off-by: George McCollister <george.mccollister@gmail.com>
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>
> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
> ---

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>

A few comments below.

> diff --git a/net/dsa/tag_xrs700x.c b/net/dsa/tag_xrs700x.c
> new file mode 100644
> index 000000000000..4ee7c260a8a9
> --- /dev/null
> +++ b/net/dsa/tag_xrs700x.c
> @@ -0,0 +1,67 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * XRS700x tag format handling
> + * Copyright (c) 2008-2009 Marvell Semiconductor

Why does Marvell get copyright?

> + * Copyright (c) 2020 NovaTech LLC
> + */
> +
> +#include <linux/etherdevice.h>
> +#include <linux/list.h>
> +#include <linux/slab.h>

These 3 includes are not needed. You can probably remove them later
though, if there is no other reason to resend.

> +#include <linux/bitops.h>
> +
> +#include "dsa_priv.h"
> +
> +static struct sk_buff *xrs700x_xmit(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct dsa_port *dp = dsa_slave_to_port(dev);
> +	u8 *trailer;
> +
> +	trailer = skb_put(skb, 1);
> +	trailer[0] = BIT(dp->index);
> +
> +	return skb;
> +}
> +
> +static struct sk_buff *xrs700x_rcv(struct sk_buff *skb, struct net_device *dev,
> +				   struct packet_type *pt)
> +{
> +	int source_port;
> +	u8 *trailer;
> +
> +	if (skb_linearize(skb))
> +		return NULL;

We've been through this, there should be no reason to linearize an skb
for a one-byte tail tag..

> +
> +	trailer = skb_tail_pointer(skb) - 1;
> +
> +	source_port = ffs((int)trailer[0]) - 1;
> +
> +	if (source_port < 0)
> +		return NULL;
> +
> +	skb->dev = dsa_master_find_slave(dev, 0, source_port);
> +	if (!skb->dev)
> +		return NULL;
> +
> +	if (pskb_trim_rcsum(skb, skb->len - 1))
> +		return NULL;
> +
> +	/* Frame is forwarded by hardware, don't forward in software. */
> +	skb->offload_fwd_mark = 1;
> +
> +	return skb;
> +}