Re: [PATCH net-next 1/2] net: dsa: tag_brcm: add support for legacy tags

[Vladimir Oltean <olteanv@gmail.com>]

On Mon, Mar 15, 2021 at 03:27:35PM +0100, Álvaro Fernández Rojas wrote:
> Add support for legacy Broadcom tags, which are similar to DSA_TAG_PROTO_BRCM.
> These tags are used on BCM5325, BCM5365 and BCM63xx switches.
> 
> Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
> ---
>  include/net/dsa.h  |  2 +
>  net/dsa/Kconfig    |  7 ++++
>  net/dsa/tag_brcm.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 105 insertions(+)
> 
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 83a933e563fe..dac303edd33d 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -49,10 +49,12 @@ struct phylink_link_state;
>  #define DSA_TAG_PROTO_XRS700X_VALUE		19
>  #define DSA_TAG_PROTO_OCELOT_8021Q_VALUE	20
>  #define DSA_TAG_PROTO_SEVILLE_VALUE		21
> +#define DSA_TAG_PROTO_BRCM_LEGACY_VALUE		22
>  
>  enum dsa_tag_protocol {
>  	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
>  	DSA_TAG_PROTO_BRCM		= DSA_TAG_PROTO_BRCM_VALUE,
> +	DSA_TAG_PROTO_BRCM_LEGACY	= DSA_TAG_PROTO_BRCM_LEGACY_VALUE,

Is there no better qualifier for this tagging protocol name than "legacy"?

>  	DSA_TAG_PROTO_BRCM_PREPEND	= DSA_TAG_PROTO_BRCM_PREPEND_VALUE,
>  	DSA_TAG_PROTO_DSA		= DSA_TAG_PROTO_DSA_VALUE,
>  	DSA_TAG_PROTO_EDSA		= DSA_TAG_PROTO_EDSA_VALUE,
> diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
> index 58b8fc82cd3c..aaf8a452fd5b 100644
> --- a/net/dsa/Kconfig
> +++ b/net/dsa/Kconfig
> @@ -48,6 +48,13 @@ config NET_DSA_TAG_BRCM
>  	  Say Y if you want to enable support for tagging frames for the
>  	  Broadcom switches which place the tag after the MAC source address.
>  
> +config NET_DSA_TAG_BRCM_LEGACY
> +	tristate "Tag driver for Broadcom legacy switches using in-frame headers"

Aren't all headers in-frame?

> +	select NET_DSA_TAG_BRCM_COMMON
> +	help
> +	  Say Y if you want to enable support for tagging frames for the
> +	  Broadcom legacy switches which place the tag after the MAC source
> +	  address.
>  
>  config NET_DSA_TAG_BRCM_PREPEND
>  	tristate "Tag driver for Broadcom switches using prepended headers"
> diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
> index e2577a7dcbca..9dbff771c9b3 100644
> --- a/net/dsa/tag_brcm.c
> +++ b/net/dsa/tag_brcm.c
> @@ -9,9 +9,23 @@
>  #include <linux/etherdevice.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
> +#include <linux/types.h>
>  
>  #include "dsa_priv.h"
>  
> +struct bcm_legacy_tag {
> +	uint16_t type;
> +#define BRCM_LEG_TYPE	0x8874
> +
> +	uint32_t tag;
> +#define BRCM_LEG_TAG_PORT_ID	(0xf)
> +#define BRCM_LEG_TAG_MULTICAST	(1 << 29)
> +#define BRCM_LEG_TAG_EGRESS	(2 << 29)
> +#define BRCM_LEG_TAG_INGRESS	(3 << 29)
> +} __attribute__((packed));
> +
> +#define BRCM_LEG_TAG_LEN	sizeof(struct bcm_legacy_tag)
> +

As Florian pointed out, tagging protocol parsing should be
endian-independent, and mapping a struct over the frame header is pretty
much not that.

>  /* This tag length is 4 bytes, older ones were 6 bytes, we do not
>   * handle them
>   */
> @@ -195,6 +209,85 @@ DSA_TAG_DRIVER(brcm_netdev_ops);
>  MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_BRCM);
>  #endif
>  
> +#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY)
> +static struct sk_buff *brcm_leg_tag_xmit(struct sk_buff *skb,
> +					 struct net_device *dev)
> +{
> +	struct dsa_port *dp = dsa_slave_to_port(dev);
> +	struct bcm_legacy_tag *brcm_tag;
> +
> +	if (skb_cow_head(skb, BRCM_LEG_TAG_LEN) < 0)
> +		return NULL;

This is not needed since commit 2f0d030c5ffe ("net: dsa: tag_brcm: let
DSA core deal with TX reallocation").

> +	/* The Ethernet switch we are interfaced with needs packets to be at
> +	 * least 64 bytes (including FCS) otherwise they will be discarded when
> +	 * they enter the switch port logic. When Broadcom tags are enabled, we
> +	 * need to make sure that packets are at least 70 bytes
> +	 * (including FCS and tag) because the length verification is done after
> +	 * the Broadcom tag is stripped off the ingress packet.
> +	 *
> +	 * Let dsa_slave_xmit() free the SKB
> +	 */
> +	if (__skb_put_padto(skb, ETH_ZLEN + BRCM_LEG_TAG_LEN, false))
> +		return NULL;

Are you sure the switches you're working on need this, or is it just
another copy-pasta?

> +	skb_push(skb, BRCM_LEG_TAG_LEN);
> +
> +	memmove(skb->data, skb->data + BRCM_LEG_TAG_LEN, 2 * ETH_ALEN);
> +
> +	brcm_tag = (struct bcm_legacy_tag *) (skb->data + 2 * ETH_ALEN);
> +
> +	brcm_tag->type = BRCM_LEG_TYPE;
> +	brcm_tag->tag = BRCM_LEG_TAG_EGRESS;
> +	brcm_tag->tag |= dp->index & BRCM_LEG_TAG_PORT_ID;
> +
> +	return skb;
> +}
> +
> +

Please remove the extra newline.

> +static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
> +					struct net_device *dev,
> +					struct packet_type *pt)
> +{
> +	int source_port;
> +	struct bcm_legacy_tag *brcm_tag;

Please declare the local variables in the order of decreasing line length.

> +
> +	if (unlikely(!pskb_may_pull(skb, BRCM_LEG_TAG_LEN)))
> +		return NULL;
> +
> +	brcm_tag = (struct bcm_legacy_tag *) (skb->data - 2);

Nitpick: the space between the *) and the (skb-> is not needed.

> +
> +	source_port = brcm_tag->tag & BRCM_LEG_TAG_PORT_ID;
> +
> +	skb->dev = dsa_master_find_slave(dev, 0, source_port);
> +	if (!skb->dev)
> +		return NULL;
> +
> +	/* Remove Broadcom tag and update checksum */
> +	skb_pull_rcsum(skb, BRCM_LEG_TAG_LEN);
> +
> +	skb->offload_fwd_mark = 1;
> +
> +	/* Move the Ethernet DA and SA */
> +	memmove(skb->data - ETH_HLEN,
> +		skb->data - ETH_HLEN - BRCM_LEG_TAG_LEN,
> +		2 * ETH_ALEN);
> +
> +	return skb;
> +}
> +
> +static const struct dsa_device_ops brcm_legacy_netdev_ops = {
> +	.name	= "brcm-legacy",
> +	.proto	= DSA_TAG_PROTO_BRCM_LEGACY,
> +	.xmit	= brcm_leg_tag_xmit,
> +	.rcv	= brcm_leg_tag_rcv,
> +	.overhead = BRCM_LEG_TAG_LEN,
> +};
> +
> +DSA_TAG_DRIVER(brcm_legacy_netdev_ops);
> +MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_BRCM_LEGACY);
> +#endif /* CONFIG_NET_DSA_TAG_BRCM_LEGACY */
> +
>  #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_PREPEND)
>  static struct sk_buff *brcm_tag_xmit_prepend(struct sk_buff *skb,
>  					     struct net_device *dev)
> @@ -227,6 +320,9 @@ static struct dsa_tag_driver *dsa_tag_driver_array[] =	{
>  #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM)
>  	&DSA_TAG_DRIVER_NAME(brcm_netdev_ops),
>  #endif
> +#if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_LEGACY)
> +	&DSA_TAG_DRIVER_NAME(brcm_legacy_netdev_ops),
> +#endif
>  #if IS_ENABLED(CONFIG_NET_DSA_TAG_BRCM_PREPEND)
>  	&DSA_TAG_DRIVER_NAME(brcm_prepend_netdev_ops),
>  #endif
> -- 
> 2.20.1
>