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

From: Andrew Lunn <[email-masked]>
Date: Fri, 15 Apr 2022 00:50:15 +0200

On Thu, Apr 14, 2022 at 02:22:40PM +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 <[email-masked]>
> ---
>  net/dsa/Kconfig          |   8 +++
>  net/dsa/Makefile         |   1 +
>  net/dsa/tag_rzn1_a5psw.c | 112 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 121 insertions(+)
>  create mode 100644 net/dsa/tag_rzn1_a5psw.c
> 
> diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
> index 8cb87b5067ee..e5b17108fa22 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
> +	  destination MAC address.
> +
>  config NET_DSA_TAG_LAN9303
>  	tristate "Tag driver for SMSC/Microchip LAN9303 family of switches"
>  	help
> @@ -159,4 +166,5 @@ config NET_DSA_TAG_XRS700X
>  	  Say Y or M if you want to enable support for tagging frames for
>  	  Arrow SpeedChips XRS700x switches that use a single byte tag trailer.
>  
> +
>  endif
> 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..7818c1c0fca2
> --- /dev/null
> +++ b/net/dsa/tag_rzn1_a5psw.c
> @@ -0,0 +1,112 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2022 Schneider Electric
> + *
> + * Clément Léger <[email-masked]>
> + */
> +
> +#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
> +#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 {
> +	u16 ctrl_tag;
> +	u16 ctrl_data;
> +	u32 ctrl_data2;
> +};
> +
> +static struct sk_buff *a5psw_tag_xmit(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct a5psw_tag *ptag, tag = {0};
> +	struct dsa_port *dp = dsa_slave_to_port(dev);
> +	u32 data2_val;

It might be worth adding a BUILD_BUG_ON(sizeof(tag) != A5PSW_TAG_LEN);

That does not cost anything at runtime, and avoids hard to find bugs
when the compiler does not do what you expect in terms of packing.

     Andrew