Re: [PATCH net-next v3 02/12] net: dsa: add Renesas RZ/N1 switch tag driver

[Vladimir Oltean <olteanv@gmail.com>]

On Wed, May 04, 2022 at 11:29:50AM +0200, Clément Léger wrote:
> The switch that is present on the Renesas RZ/N1 SoC uses a specific
> VLAN value followed by 6 bytes which contains forwarding configuration.
> 
> Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> ---
>  include/net/dsa.h        |   2 +
>  net/dsa/Kconfig          |   7 +++
>  net/dsa/Makefile         |   1 +
>  net/dsa/tag_rzn1_a5psw.c | 114 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 124 insertions(+)
>  create mode 100644 net/dsa/tag_rzn1_a5psw.c
> 
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index d9da32aacbf1..9aaaa7deb102 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -53,6 +53,7 @@ struct phylink_link_state;
>  #define DSA_TAG_PROTO_SJA1110_VALUE		23
>  #define DSA_TAG_PROTO_RTL8_4_VALUE		24
>  #define DSA_TAG_PROTO_RTL8_4T_VALUE		25
> +#define DSA_TAG_PROTO_RZN1_A5PSW_VALUE		26
>  
>  enum dsa_tag_protocol {
>  	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
> @@ -81,6 +82,7 @@ enum dsa_tag_protocol {
>  	DSA_TAG_PROTO_SJA1110		= DSA_TAG_PROTO_SJA1110_VALUE,
>  	DSA_TAG_PROTO_RTL8_4		= DSA_TAG_PROTO_RTL8_4_VALUE,
>  	DSA_TAG_PROTO_RTL8_4T		= DSA_TAG_PROTO_RTL8_4T_VALUE,
> +	DSA_TAG_PROTO_RZN1_A5PSW	= DSA_TAG_PROTO_RZN1_A5PSW_VALUE,
>  };
>  
>  struct dsa_switch;
> diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
> index 8cb87b5067ee..e22f33d7cf60 100644
> --- a/net/dsa/Kconfig
> +++ b/net/dsa/Kconfig
> @@ -132,6 +132,13 @@ config NET_DSA_TAG_RTL8_4
>  	  Say Y or M if you want to enable support for tagging frames for Realtek
>  	  switches with 8 byte protocol 4 tags, such as the Realtek RTL8365MB-VC.
>  
> +config NET_DSA_TAG_RZN1_A5PSW
> +	tristate "Tag driver for Renesas RZ/N1 A5PSW switch"
> +	help
> +	  Say Y or M if you want to enable support for tagging frames for
> +	  Renesas RZ/N1 embedded switch that uses a 8 byte tag located after

"an" 8 byte tag

> +	  destination MAC address.
> +
>  config NET_DSA_TAG_LAN9303
>  	tristate "Tag driver for SMSC/Microchip LAN9303 family of switches"
>  	help
> diff --git a/net/dsa/Makefile b/net/dsa/Makefile
> index 9f75820e7c98..af28c24ead18 100644
> --- a/net/dsa/Makefile
> +++ b/net/dsa/Makefile
> @@ -17,6 +17,7 @@ obj-$(CONFIG_NET_DSA_TAG_OCELOT_8021Q) += tag_ocelot_8021q.o
>  obj-$(CONFIG_NET_DSA_TAG_QCA) += tag_qca.o
>  obj-$(CONFIG_NET_DSA_TAG_RTL4_A) += tag_rtl4_a.o
>  obj-$(CONFIG_NET_DSA_TAG_RTL8_4) += tag_rtl8_4.o
> +obj-$(CONFIG_NET_DSA_TAG_RZN1_A5PSW) += tag_rzn1_a5psw.o
>  obj-$(CONFIG_NET_DSA_TAG_SJA1105) += tag_sja1105.o
>  obj-$(CONFIG_NET_DSA_TAG_TRAILER) += tag_trailer.o
>  obj-$(CONFIG_NET_DSA_TAG_XRS700X) += tag_xrs700x.o
> diff --git a/net/dsa/tag_rzn1_a5psw.c b/net/dsa/tag_rzn1_a5psw.c
> new file mode 100644
> index 000000000000..87177682eb54
> --- /dev/null
> +++ b/net/dsa/tag_rzn1_a5psw.c
> @@ -0,0 +1,114 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2022 Schneider Electric
> + *
> + * Clément Léger <clement.leger@bootlin.com>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/etherdevice.h>
> +#include <net/dsa.h>
> +
> +#include "dsa_priv.h"
> +
> +/* To define the outgoing port and to discover the incoming port a TAG is
> + * inserted after Src MAC :
> + *
> + *       Dest MAC       Src MAC           TAG         Type
> + * ...| 1 2 3 4 5 6 | 1 2 3 4 5 6 | 1 2 3 4 5 6 7 8 | 1 2 |...
> + *                                |<--------------->|
> + *
> + * See struct a5psw_tag for layout
> + */
> +
> +#define A5PSW_TAG_VALUE			0xE001

Maybe an ETH_P_DSA_A5PSW definition in include/uapi/linux/if_ether.h
would be appropriate? I'm not sure.

> +#define A5PSW_TAG_LEN			8
> +#define A5PSW_CTRL_DATA_FORCE_FORWARD	BIT(0)
> +/* This is both used for xmit tag and rcv tagging */
> +#define A5PSW_CTRL_DATA_PORT		GENMASK(3, 0)
> +
> +struct a5psw_tag {
> +	__be16 ctrl_tag;
> +	__be16 ctrl_data;
> +	__be16 ctrl_data2_hi;
> +	__be16 ctrl_data2_lo;
> +};
> +
> +static struct sk_buff *a5psw_tag_xmit(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct dsa_port *dp = dsa_slave_to_port(dev);
> +	struct a5psw_tag *ptag;
> +	u32 data2_val;
> +
> +	BUILD_BUG_ON(sizeof(*ptag) != A5PSW_TAG_LEN);
> +
> +	/* 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 tagging is enabled, we need
> +	 * to make sure that packets are at least 70 bytes (including FCS and
> +	 * tag).
> +	 */
> +	if (__skb_put_padto(skb, ETH_ZLEN + ETH_FCS_LEN + A5PSW_TAG_LEN, false))
> +		return NULL;

I'm confused by the inclusion of the FCS length in this calculation,
since the FCS space isn't present in the skb buffer as far as I know?

"64 bytes including FCS" means "60 bytes excluding FCS".
And ETH_ZLEN is 60...

And I'm also not sure how we got to the number 70? A5PSW_TAG_LEN is 8.
If we add it to 60 we get 68. If we add it to 64 we get 72?

> +
> +	/* provide 'A5PSW_TAG_LEN' bytes additional space */
> +	skb_push(skb, A5PSW_TAG_LEN);
> +
> +	/* make room between MACs and Ether-Type to insert tag */
> +	dsa_alloc_etype_header(skb, A5PSW_TAG_LEN);
> +
> +	ptag = dsa_etype_header_pos_tx(skb);
> +
> +	data2_val = FIELD_PREP(A5PSW_CTRL_DATA_PORT, BIT(dp->index));
> +	ptag->ctrl_tag = htons(A5PSW_TAG_VALUE);
> +	ptag->ctrl_data = htons(A5PSW_CTRL_DATA_FORCE_FORWARD);
> +	ptag->ctrl_data2_lo = htons(data2_val);
> +	ptag->ctrl_data2_hi = 0;
> +
> +	return skb;
> +}
> +
> +static struct sk_buff *a5psw_tag_rcv(struct sk_buff *skb,
> +				     struct net_device *dev)
> +{
> +	struct a5psw_tag *tag;
> +	int port;
> +
> +	if (unlikely(!pskb_may_pull(skb, A5PSW_TAG_LEN))) {
> +		dev_warn_ratelimited(&dev->dev,
> +				     "Dropping packet, cannot pull\n");
> +		return NULL;
> +	}
> +
> +	tag = dsa_etype_header_pos_rx(skb);
> +
> +	if (tag->ctrl_tag != htons(A5PSW_TAG_VALUE)) {
> +		dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid TAG marker\n");
> +		return NULL;
> +	}
> +
> +	port = FIELD_GET(A5PSW_CTRL_DATA_PORT, ntohs(tag->ctrl_data));
> +
> +	skb->dev = dsa_master_find_slave(dev, 0, port);
> +	if (!skb->dev)
> +		return NULL;
> +
> +	skb_pull_rcsum(skb, A5PSW_TAG_LEN);
> +	dsa_strip_etype_header(skb, A5PSW_TAG_LEN);
> +
> +	dsa_default_offload_fwd_mark(skb);
> +
> +	return skb;
> +}
> +
> +static const struct dsa_device_ops a5psw_netdev_ops = {
> +	.name	= "a5psw",
> +	.proto	= DSA_TAG_PROTO_RZN1_A5PSW,
> +	.xmit	= a5psw_tag_xmit,
> +	.rcv	= a5psw_tag_rcv,
> +	.needed_headroom = A5PSW_TAG_LEN,
> +};
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_A5PSW);
> +module_dsa_tag_driver(a5psw_netdev_ops);
> -- 
> 2.34.1
>