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Message-ID: <20251216203935.z5ss4sxbt6xc2444@skbuf>
Date: Tue, 16 Dec 2025 22:39:35 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Heiner Kallweit <hkallweit1@...il.com>,
Russell King <linux@...linux.org.uk>,
Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
Frank Wunderlich <frankwu@....de>, Chad Monroe <chad@...roe.io>,
Cezary Wilmanski <cezary.wilmanski@...ran.com>,
Avinash Jayaraman <ajayaraman@...linear.com>,
Bing tao Xu <bxu@...linear.com>, Liang Xu <lxu@...linear.com>,
Juraj Povazanec <jpovazanec@...linear.com>,
"Fanni (Fang-Yi) Chan" <fchan@...linear.com>,
"Benny (Ying-Tsan) Weng" <yweng@...linear.com>,
"Livia M. Rosu" <lrosu@...linear.com>,
John Crispin <john@...ozen.org>
Subject: Re: [PATCH RFC net-next v3 2/4] net: dsa: add tag formats for
MxL862xx switches
On Mon, Dec 15, 2025 at 12:11:43AM +0000, Daniel Golle wrote:
> Add proprietary special tag format for the MaxLinear MXL862xx family of
> switches. While using the same Ethertype as MaxLinear's GSW1xx swtiches,
s/swtiches/switches/
> the actual tag format differs significantly, hence we need a dedicated
> tag driver for that.
Reusing the same EtherType for two different DSA tagging protocols is
very bad news, possibly with implications also for libpcap. Is the
EtherType configurable in the MXL862xx family?
>
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> ---
> RFC v3: no changes
> RFC v2: make sure all tag fields are initialized
>
> MAINTAINERS | 1 +
> include/net/dsa.h | 2 +
> net/dsa/Kconfig | 7 +++
> net/dsa/Makefile | 1 +
> net/dsa/tag_mxl862xx.c | 113 +++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 124 insertions(+)
> create mode 100644 net/dsa/tag_mxl862xx.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c433a15d9797a..a20498cc8320b 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -15609,6 +15609,7 @@ M: Daniel Golle <daniel@...rotopia.org>
> L: netdev@...r.kernel.org
> S: Maintained
> F: Documentation/devicetree/bindings/net/dsa/maxlinear,mxl862xx.yaml
> +F: net/dsa/tag_mxl862xx.c
>
> MCAN DEVICE DRIVER
> M: Markus Schneider-Pargmann <msp@...libre.com>
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index e40cdc12f7f39..e4c2b47a2a46e 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -57,6 +57,7 @@ struct tc_action;
> #define DSA_TAG_PROTO_BRCM_LEGACY_FCS_VALUE 29
> #define DSA_TAG_PROTO_YT921X_VALUE 30
> #define DSA_TAG_PROTO_MXL_GSW1XX_VALUE 31
> +#define DSA_TAG_PROTO_MXL862_VALUE 32
>
> enum dsa_tag_protocol {
> DSA_TAG_PROTO_NONE = DSA_TAG_PROTO_NONE_VALUE,
> @@ -91,6 +92,7 @@ enum dsa_tag_protocol {
> DSA_TAG_PROTO_VSC73XX_8021Q = DSA_TAG_PROTO_VSC73XX_8021Q_VALUE,
> DSA_TAG_PROTO_YT921X = DSA_TAG_PROTO_YT921X_VALUE,
> DSA_TAG_PROTO_MXL_GSW1XX = DSA_TAG_PROTO_MXL_GSW1XX_VALUE,
> + DSA_TAG_PROTO_MXL862 = DSA_TAG_PROTO_MXL862_VALUE,
> };
>
> struct dsa_switch;
> diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
> index f86b30742122f..c897d62326f5b 100644
> --- a/net/dsa/Kconfig
> +++ b/net/dsa/Kconfig
> @@ -145,6 +145,13 @@ config NET_DSA_TAG_QCA
> Say Y or M if you want to enable support for tagging frames for
> the Qualcomm Atheros QCA8K switches.
>
> +config NET_DSA_TAG_MXL862
> + tristate "Tag driver for MxL862xx switches"
> + help
> + Say Y or M if you want to enable support for tagging frames for the
> + Maxlinear MxL86252 and MxL86282 switches using their native 8-byte
MaxLinear with capital L
> + tagging protocol.
> +
> config NET_DSA_TAG_RTL4_A
> tristate "Tag driver for Realtek 4 byte protocol A tags"
> help
> diff --git a/net/dsa/Makefile b/net/dsa/Makefile
> index 42d173f5a7013..dbe2a742e3322 100644
> --- a/net/dsa/Makefile
> +++ b/net/dsa/Makefile
> @@ -28,6 +28,7 @@ obj-$(CONFIG_NET_DSA_TAG_HELLCREEK) += tag_hellcreek.o
> obj-$(CONFIG_NET_DSA_TAG_KSZ) += tag_ksz.o
> obj-$(CONFIG_NET_DSA_TAG_LAN9303) += tag_lan9303.o
> obj-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o
> +obj-$(CONFIG_NET_DSA_TAG_MXL862) += tag_mxl862xx.o
> obj-$(CONFIG_NET_DSA_TAG_MXL_GSW1XX) += tag_mxl-gsw1xx.o
> obj-$(CONFIG_NET_DSA_TAG_NONE) += tag_none.o
> obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o
> diff --git a/net/dsa/tag_mxl862xx.c b/net/dsa/tag_mxl862xx.c
> new file mode 100644
> index 0000000000000..9c5e5f90dcb63
> --- /dev/null
> +++ b/net/dsa/tag_mxl862xx.c
> @@ -0,0 +1,113 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * DSA Special Tag for MaxLinear 862xx switch chips
> + *
> + * Copyright (C) 2025 Daniel Golle <daniel@...rotopia.org>
> + * Copyright (C) 2024 MaxLinear Inc.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/etherdevice.h>
> +#include <linux/skbuff.h>
> +#include <net/dsa.h>
> +#include "tag.h"
> +
> +#define MXL862_NAME "mxl862xx"
> +
> +/* To define the outgoing port and to discover the incoming port a special
> + * tag is used by the GSW1xx.
> + *
> + * Dest MAC Src MAC special TAG EtherType
> + * ...| 1 2 3 4 5 6 | 1 2 3 4 5 6 | 1 2 3 4 5 6 7 8 | 1 2 |...
> + * |<--------------->|
> + */
> +
> +#define MXL862_HEADER_LEN 8
> +
> +/* Byte 7 */
> +#define MXL862_IGP_EGP GENMASK(3, 0)
> +
> +static struct sk_buff *mxl862_tag_xmit(struct sk_buff *skb,
> + struct net_device *dev)
> +{
> + struct dsa_port *dp = dsa_user_to_port(dev);
> + struct dsa_port *cpu_dp = dp->cpu_dp;
> + unsigned int cpu_port = cpu_dp->index + 1;
> + unsigned int usr_port = dp->index + 1;
> + __be16 *mxl862_tag;
> +
> + if (!skb)
> + return skb;
> +
> + /* provide additional space 'MXL862_HEADER_LEN' bytes */
> + skb_push(skb, MXL862_HEADER_LEN);
> +
> + /* shift MAC address to the beginnig of the enlarged buffer,
> + * releasing the space required for DSA tag (between MAC address and
> + * Ethertype)
> + */
> + dsa_alloc_etype_header(skb, MXL862_HEADER_LEN);
> +
> + /* special tag ingress */
> + mxl862_tag = dsa_etype_header_pos_tx(skb);
> + mxl862_tag[0] = htons(ETH_P_MXLGSW);
> + mxl862_tag[1] = 0;
> + mxl862_tag[2] = htons(usr_port + 16 - cpu_port);
Can you place a comment on the meaning of these port manipulations
(cpu_dp->index + 1, dp->index + 1, usr_port + 16 - cpu_port,
port = port - 1 in rcv())?
> + mxl862_tag[3] = htons(FIELD_PREP(MXL862_IGP_EGP, cpu_port));
> +
> + return skb;
> +}
> +
> +static struct sk_buff *mxl862_tag_rcv(struct sk_buff *skb,
> + struct net_device *dev)
> +{
> + int port;
> + __be16 *mxl862_tag;
> +
> + if (unlikely(!pskb_may_pull(skb, MXL862_HEADER_LEN))) {
> + dev_warn_ratelimited(&dev->dev, "Cannot pull SKB, packet dropped\n");
> + return NULL;
> + }
> +
> + mxl862_tag = dsa_etype_header_pos_rx(skb);
> +
> + if (unlikely(mxl862_tag[0] != htons(ETH_P_MXLGSW))) {
> + dev_warn_ratelimited(&dev->dev, "Invalid special tag marker, packet dropped\n");
> + dev_warn_ratelimited(&dev->dev, "Rx Packet Tag: %8ph\n",
> + mxl862_tag);
> + return NULL;
> + }
> +
> + /* Get source port information */
> + port = FIELD_GET(MXL862_IGP_EGP, ntohs(mxl862_tag[3]));
> + port = port - 1;
> + skb->dev = dsa_conduit_find_user(dev, 0, port);
> + if (!skb->dev) {
> + dev_warn_ratelimited(&dev->dev, "Invalid source port, packet dropped\n");
> + dev_warn_ratelimited(&dev->dev, "Rx Packet Tag: %8ph\n",
> + mxl862_tag);
> + return NULL;
> + }
> +
> + /* remove the MxL862xx special tag between the MAC addresses and the
> + * current ethertype field.
> + */
> + skb_pull_rcsum(skb, MXL862_HEADER_LEN);
> + dsa_strip_etype_header(skb, MXL862_HEADER_LEN);
> +
> + return skb;
> +}
> +
> +static const struct dsa_device_ops mxl862_netdev_ops = {
> + .name = "mxl862",
> + .proto = DSA_TAG_PROTO_MXL862,
> + .xmit = mxl862_tag_xmit,
> + .rcv = mxl862_tag_rcv,
> + .needed_headroom = MXL862_HEADER_LEN,
> +};
> +
> +MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_MXL862, MXL862_NAME);
> +MODULE_DESCRIPTION("DSA tag driver for MaxLinear MxL862xx switches");
> +MODULE_LICENSE("GPL");
> +
> +module_dsa_tag_driver(mxl862_netdev_ops);
> --
> 2.52.0
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