diff mbox series

[v2,net-next,4/6] net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag

Message ID 20211013145040.886956-5-alvin@pqrs.dk (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series net: dsa: add support for RTL8365MB-VC | expand

Checks

Context Check Description
netdev/cover_letter success Series has a cover letter
netdev/fixes_present success Fixes tag not required for -next series
netdev/patch_count success Link
netdev/tree_selection success Clearly marked for net-next
netdev/subject_prefix success Link
netdev/cc_maintainers success CCed 7 of 7 maintainers
netdev/source_inline success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/module_param success Was 0 now: 0
netdev/build_32bit fail Errors and warnings before: 8 this patch: 14
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/verify_fixes success No Fixes tag
netdev/checkpatch warning WARNING: added, moved or deleted file(s), does MAINTAINERS need updating? WARNING: please write a paragraph that describes the config symbol fully
netdev/build_allmodconfig_warn fail Errors and warnings before: 8 this patch: 14
netdev/header_inline success No static functions without inline keyword in header files

Commit Message

Alvin Šipraga Oct. 13, 2021, 2:50 p.m. UTC 
From: Alvin Šipraga <alsi@bang-olufsen.dk>

This commit implements a basic version of the 8 byte tag protocol used
in the Realtek RTL8365MB-VC unmanaged switch, which carries with it a
protocol version of 0x04.

The implementation itself only handles the parsing of the EtherType
value and Realtek protocol version, together with the source or
destination port fields. The rest is left unimplemented for now.

The tag format is described in a confidential document provided to my
company by Realtek Semiconductor Corp. Permission has been granted by
the vendor to publish this driver based on that material, together with
an extract from the document describing the tag format and its fields.
It is hoped that this will help future implementors who do not have
access to the material but who wish to extend the functionality of
drivers for chips which use this protocol.

In addition, two possible values of the REASON field are specified,
based on experiments on my end. Realtek does not specify what value this
field can take.

Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---

v1 -> v2:
  - collect Reviewed-by from Vladimir and Linus
  - don't set default fwd_offload_mark if packet is trapped to CPU
  - use #defines and FIELD_* macros to make Linus happy

RFC -> v1:
  - minor changes to the big comment at the top, including some
    empirical information about the REASON code
  - use dev_*_ratelimited() instead of netdev_*() for logging
  - use warning instead of debug messages
  - use ETH_P_REALTEK from if_ether.h
  - set LEARN_DIS on xmit
  - remove superfluous variables/expressions and use __b16 for tag
    variable
  - use new helper functions to insert/remove CPU tag
  - set offload_fwd_mark properly using helper function

 include/net/dsa.h    |   2 +
 net/dsa/Kconfig      |   6 ++
 net/dsa/Makefile     |   1 +
 net/dsa/tag_rtl8_4.c | 184 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 193 insertions(+)
 create mode 100644 net/dsa/tag_rtl8_4.c

Comments

kernel test robot Oct. 14, 2021, 12:38 a.m. UTC | #1 
Hi "Alvin,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Alvin-ipraga/net-dsa-add-support-for-RTL8365MB-VC/20211013-225955
base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git d1f24712a86abd04d82cf4b00fb4ab8ff2d23c8a
config: x86_64-randconfig-r034-20211013 (attached as .config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project b6a8c695542b2987eb9a203d5663a0740cb4725f)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/e17d422e49ba2acbf43ae144fcce940cc06152a0
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Alvin-ipraga/net-dsa-add-support-for-RTL8365MB-VC/20211013-225955
        git checkout e17d422e49ba2acbf43ae144fcce940cc06152a0
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> net/dsa/tag_rtl8_4.c:108:17: error: implicit declaration of function 'FIELD_PREP' [-Werror,-Wimplicit-function-declaration]
           tag[1] = htons(FIELD_PREP(RTL8_4_PROTOCOL, RTL8_4_PROTOCOL_RTL8365MB));
                          ^
>> net/dsa/tag_rtl8_4.c:142:10: error: implicit declaration of function 'FIELD_GET' [-Werror,-Wimplicit-function-declaration]
           proto = FIELD_GET(RTL8_4_PROTOCOL, ntohs(tag[1]));
                   ^
   2 errors generated.


vim +/FIELD_PREP +108 net/dsa/tag_rtl8_4.c

    85	
    86	static struct sk_buff *rtl8_4_tag_xmit(struct sk_buff *skb,
    87					       struct net_device *dev)
    88	{
    89		struct dsa_port *dp = dsa_slave_to_port(dev);
    90		__be16 *tag;
    91	
    92		/* Pad out so the (stripped) packet is at least 64 bytes long
    93		 * (including FCS), otherwise the switch will drop the packet.
    94		 * Then we need an additional 8 bytes for the Realtek tag.
    95		 */
    96		if (unlikely(__skb_put_padto(skb, ETH_ZLEN + RTL8_4_TAG_LEN, false)))
    97			return NULL;
    98	
    99		skb_push(skb, RTL8_4_TAG_LEN);
   100	
   101		dsa_alloc_etype_header(skb, RTL8_4_TAG_LEN);
   102		tag = dsa_etype_header_pos_tx(skb);
   103	
   104		/* Set Realtek EtherType */
   105		tag[0] = htons(ETH_P_REALTEK);
   106	
   107		/* Set Protocol; zero REASON */
 > 108		tag[1] = htons(FIELD_PREP(RTL8_4_PROTOCOL, RTL8_4_PROTOCOL_RTL8365MB));
   109	
   110		/* Zero FID_EN, FID, PRI_EN, PRI, KEEP; set LEARN_DIS */
   111		tag[2] = htons(FIELD_PREP(RTL8_4_LEARN_DIS, 1));
   112	
   113		/* Zero ALLOW; set RX (CPU->switch) forwarding port mask */
   114		tag[3] = htons(FIELD_PREP(RTL8_4_RX, BIT(dp->index)));
   115	
   116		return skb;
   117	}
   118	
   119	static struct sk_buff *rtl8_4_tag_rcv(struct sk_buff *skb,
   120					      struct net_device *dev)
   121	{
   122		__be16 *tag;
   123		u16 etype;
   124		u8 reason;
   125		u8 proto;
   126		u8 port;
   127	
   128		if (unlikely(!pskb_may_pull(skb, RTL8_4_TAG_LEN)))
   129			return NULL;
   130	
   131		tag = dsa_etype_header_pos_rx(skb);
   132	
   133		/* Parse Realtek EtherType */
   134		etype = ntohs(tag[0]);
   135		if (unlikely(etype != ETH_P_REALTEK)) {
   136			dev_warn_ratelimited(&dev->dev,
   137					     "non-realtek ethertype 0x%04x\n", etype);
   138			return NULL;
   139		}
   140	
   141		/* Parse Protocol */
 > 142		proto = FIELD_GET(RTL8_4_PROTOCOL, ntohs(tag[1]));
   143		if (unlikely(proto != RTL8_4_PROTOCOL_RTL8365MB)) {
   144			dev_warn_ratelimited(&dev->dev,
   145					     "unknown realtek protocol 0x%02x\n",
   146					     proto);
   147			return NULL;
   148		}
   149	
   150		/* Parse REASON */
   151		reason = FIELD_GET(RTL8_4_REASON, ntohs(tag[1]));
   152	
   153		/* Parse TX (switch->CPU) */
   154		port = FIELD_GET(RTL8_4_TX, ntohs(tag[3]));
   155		skb->dev = dsa_master_find_slave(dev, 0, port);
   156		if (!skb->dev) {
   157			dev_warn_ratelimited(&dev->dev,
   158					     "could not find slave for port %d\n",
   159					     port);
   160			return NULL;
   161		}
   162	
   163		/* Remove tag and recalculate checksum */
   164		skb_pull_rcsum(skb, RTL8_4_TAG_LEN);
   165	
   166		dsa_strip_etype_header(skb, RTL8_4_TAG_LEN);
   167	
   168		if (reason != RTL8_4_REASON_TRAP)
   169			dsa_default_offload_fwd_mark(skb);
   170	
   171		return skb;
   172	}
   173	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
kernel test robot Oct. 14, 2021, 12:46 a.m. UTC | #2 
Hi "Alvin,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Alvin-ipraga/net-dsa-add-support-for-RTL8365MB-VC/20211013-225955
base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git d1f24712a86abd04d82cf4b00fb4ab8ff2d23c8a
config: powerpc-randconfig-r023-20211013 (attached as .config)
compiler: powerpc-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/e17d422e49ba2acbf43ae144fcce940cc06152a0
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Alvin-ipraga/net-dsa-add-support-for-RTL8365MB-VC/20211013-225955
        git checkout e17d422e49ba2acbf43ae144fcce940cc06152a0
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=powerpc 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   In file included from include/linux/byteorder/big_endian.h:5,
                    from arch/powerpc/include/uapi/asm/byteorder.h:14,
                    from include/asm-generic/bitops/le.h:7,
                    from arch/powerpc/include/asm/bitops.h:265,
                    from include/linux/bitops.h:33,
                    from include/linux/kernel.h:12,
                    from include/linux/skbuff.h:13,
                    from include/linux/if_ether.h:19,
                    from include/linux/etherdevice.h:20,
                    from net/dsa/tag_rtl8_4.c:64:
   net/dsa/tag_rtl8_4.c: In function 'rtl8_4_tag_xmit':
>> net/dsa/tag_rtl8_4.c:108:24: error: implicit declaration of function 'FIELD_PREP' [-Werror=implicit-function-declaration]
     108 |         tag[1] = htons(FIELD_PREP(RTL8_4_PROTOCOL, RTL8_4_PROTOCOL_RTL8365MB));
         |                        ^~~~~~~~~~
   include/uapi/linux/byteorder/big_endian.h:41:51: note: in definition of macro '__cpu_to_be16'
      41 | #define __cpu_to_be16(x) ((__force __be16)(__u16)(x))
         |                                                   ^
   include/linux/byteorder/generic.h:141:18: note: in expansion of macro '___htons'
     141 | #define htons(x) ___htons(x)
         |                  ^~~~~~~~
   net/dsa/tag_rtl8_4.c:108:18: note: in expansion of macro 'htons'
     108 |         tag[1] = htons(FIELD_PREP(RTL8_4_PROTOCOL, RTL8_4_PROTOCOL_RTL8365MB));
         |                  ^~~~~
   net/dsa/tag_rtl8_4.c: In function 'rtl8_4_tag_rcv':
>> net/dsa/tag_rtl8_4.c:142:17: error: implicit declaration of function 'FIELD_GET'; did you mean 'FOLL_GET'? [-Werror=implicit-function-declaration]
     142 |         proto = FIELD_GET(RTL8_4_PROTOCOL, ntohs(tag[1]));
         |                 ^~~~~~~~~
         |                 FOLL_GET
   cc1: some warnings being treated as errors


vim +/FIELD_PREP +108 net/dsa/tag_rtl8_4.c

  > 64	#include <linux/etherdevice.h>
    65	
    66	#include "dsa_priv.h"
    67	
    68	/* Protocols supported:
    69	 *
    70	 * 0x04 = RTL8365MB DSA protocol
    71	 */
    72	
    73	#define RTL8_4_TAG_LEN			8
    74	
    75	#define RTL8_4_PROTOCOL			GENMASK(15, 8)
    76	#define   RTL8_4_PROTOCOL_RTL8365MB	0x04
    77	#define RTL8_4_REASON			GENMASK(7, 0)
    78	#define   RTL8_4_REASON_FORWARD		0
    79	#define   RTL8_4_REASON_TRAP		80
    80	
    81	#define RTL8_4_LEARN_DIS		BIT(5)
    82	
    83	#define RTL8_4_TX			GENMASK(3, 0)
    84	#define RTL8_4_RX			GENMASK(10, 0)
    85	
    86	static struct sk_buff *rtl8_4_tag_xmit(struct sk_buff *skb,
    87					       struct net_device *dev)
    88	{
    89		struct dsa_port *dp = dsa_slave_to_port(dev);
    90		__be16 *tag;
    91	
    92		/* Pad out so the (stripped) packet is at least 64 bytes long
    93		 * (including FCS), otherwise the switch will drop the packet.
    94		 * Then we need an additional 8 bytes for the Realtek tag.
    95		 */
    96		if (unlikely(__skb_put_padto(skb, ETH_ZLEN + RTL8_4_TAG_LEN, false)))
    97			return NULL;
    98	
    99		skb_push(skb, RTL8_4_TAG_LEN);
   100	
   101		dsa_alloc_etype_header(skb, RTL8_4_TAG_LEN);
   102		tag = dsa_etype_header_pos_tx(skb);
   103	
   104		/* Set Realtek EtherType */
   105		tag[0] = htons(ETH_P_REALTEK);
   106	
   107		/* Set Protocol; zero REASON */
 > 108		tag[1] = htons(FIELD_PREP(RTL8_4_PROTOCOL, RTL8_4_PROTOCOL_RTL8365MB));
   109	
   110		/* Zero FID_EN, FID, PRI_EN, PRI, KEEP; set LEARN_DIS */
   111		tag[2] = htons(FIELD_PREP(RTL8_4_LEARN_DIS, 1));
   112	
   113		/* Zero ALLOW; set RX (CPU->switch) forwarding port mask */
   114		tag[3] = htons(FIELD_PREP(RTL8_4_RX, BIT(dp->index)));
   115	
   116		return skb;
   117	}
   118	
   119	static struct sk_buff *rtl8_4_tag_rcv(struct sk_buff *skb,
   120					      struct net_device *dev)
   121	{
   122		__be16 *tag;
   123		u16 etype;
   124		u8 reason;
   125		u8 proto;
   126		u8 port;
   127	
   128		if (unlikely(!pskb_may_pull(skb, RTL8_4_TAG_LEN)))
   129			return NULL;
   130	
   131		tag = dsa_etype_header_pos_rx(skb);
   132	
   133		/* Parse Realtek EtherType */
   134		etype = ntohs(tag[0]);
   135		if (unlikely(etype != ETH_P_REALTEK)) {
   136			dev_warn_ratelimited(&dev->dev,
   137					     "non-realtek ethertype 0x%04x\n", etype);
   138			return NULL;
   139		}
   140	
   141		/* Parse Protocol */
 > 142		proto = FIELD_GET(RTL8_4_PROTOCOL, ntohs(tag[1]));
   143		if (unlikely(proto != RTL8_4_PROTOCOL_RTL8365MB)) {
   144			dev_warn_ratelimited(&dev->dev,
   145					     "unknown realtek protocol 0x%02x\n",
   146					     proto);
   147			return NULL;
   148		}
   149	
   150		/* Parse REASON */
   151		reason = FIELD_GET(RTL8_4_REASON, ntohs(tag[1]));
   152	
   153		/* Parse TX (switch->CPU) */
   154		port = FIELD_GET(RTL8_4_TX, ntohs(tag[3]));
   155		skb->dev = dsa_master_find_slave(dev, 0, port);
   156		if (!skb->dev) {
   157			dev_warn_ratelimited(&dev->dev,
   158					     "could not find slave for port %d\n",
   159					     port);
   160			return NULL;
   161		}
   162	
   163		/* Remove tag and recalculate checksum */
   164		skb_pull_rcsum(skb, RTL8_4_TAG_LEN);
   165	
   166		dsa_strip_etype_header(skb, RTL8_4_TAG_LEN);
   167	
   168		if (reason != RTL8_4_REASON_TRAP)
   169			dsa_default_offload_fwd_mark(skb);
   170	
   171		return skb;
   172	}
   173	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
Florian Fainelli Oct. 14, 2021, 2:19 a.m. UTC | #3 
On 10/13/2021 7:50 AM, Alvin Šipraga wrote:
> From: Alvin Šipraga <alsi@bang-olufsen.dk>
> 
> This commit implements a basic version of the 8 byte tag protocol used
> in the Realtek RTL8365MB-VC unmanaged switch, which carries with it a
> protocol version of 0x04.
> 
> The implementation itself only handles the parsing of the EtherType
> value and Realtek protocol version, together with the source or
> destination port fields. The rest is left unimplemented for now.
> 
> The tag format is described in a confidential document provided to my
> company by Realtek Semiconductor Corp. Permission has been granted by
> the vendor to publish this driver based on that material, together with
> an extract from the document describing the tag format and its fields.
> It is hoped that this will help future implementors who do not have
> access to the material but who wish to extend the functionality of
> drivers for chips which use this protocol.
> 
> In addition, two possible values of the REASON field are specified,
> based on experiments on my end. Realtek does not specify what value this
> field can take.
> 
> Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
> Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
diff mbox series

Patch

diff --git a/include/net/dsa.h b/include/net/dsa.h
index d784e76113b8..783060e851a9 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -51,6 +51,7 @@  struct phylink_link_state;
 #define DSA_TAG_PROTO_SEVILLE_VALUE		21
 #define DSA_TAG_PROTO_BRCM_LEGACY_VALUE		22
 #define DSA_TAG_PROTO_SJA1110_VALUE		23
+#define DSA_TAG_PROTO_RTL8_4_VALUE		24
 
 enum dsa_tag_protocol {
 	DSA_TAG_PROTO_NONE		= DSA_TAG_PROTO_NONE_VALUE,
@@ -77,6 +78,7 @@  enum dsa_tag_protocol {
 	DSA_TAG_PROTO_OCELOT_8021Q	= DSA_TAG_PROTO_OCELOT_8021Q_VALUE,
 	DSA_TAG_PROTO_SEVILLE		= DSA_TAG_PROTO_SEVILLE_VALUE,
 	DSA_TAG_PROTO_SJA1110		= DSA_TAG_PROTO_SJA1110_VALUE,
+	DSA_TAG_PROTO_RTL8_4		= DSA_TAG_PROTO_RTL8_4_VALUE,
 };
 
 struct dsa_switch;
diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index 6c7f79e45886..57fc52b17d55 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -130,6 +130,12 @@  config NET_DSA_TAG_RTL4_A
 	  Realtek switches with 4 byte protocol A tags, sich as found in
 	  the Realtek RTL8366RB.
 
+config NET_DSA_TAG_RTL8_4
+	tristate "Tag driver for Realtek 8 byte protocol 4 tags"
+	help
+	  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_LAN9303
 	tristate "Tag driver for SMSC/Microchip LAN9303 family of switches"
 	help
diff --git a/net/dsa/Makefile b/net/dsa/Makefile
index f78d537044db..9f75820e7c98 100644
--- a/net/dsa/Makefile
+++ b/net/dsa/Makefile
@@ -16,6 +16,7 @@  obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o
 obj-$(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_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_rtl8_4.c b/net/dsa/tag_rtl8_4.c
new file mode 100644
index 000000000000..8dbdefe47289
--- /dev/null
+++ b/net/dsa/tag_rtl8_4.c
@@ -0,0 +1,184 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Handler for Realtek 8 byte switch tags
+ *
+ * Copyright (C) 2021 Alvin Šipraga <alsi@bang-olufsen.dk>
+ *
+ * NOTE: Currently only supports protocol "4" found in the RTL8365MB, hence
+ * named tag_rtl8_4.
+ *
+ * This tag header has the following format:
+ *
+ *  -------------------------------------------
+ *  | MAC DA | MAC SA | 8 byte tag | Type | ...
+ *  -------------------------------------------
+ *     _______________/            \______________________________________
+ *    /                                                                   \
+ *  0                                  7|8                                 15
+ *  |-----------------------------------+-----------------------------------|---
+ *  |                               (16-bit)                                | ^
+ *  |                       Realtek EtherType [0x8899]                      | |
+ *  |-----------------------------------+-----------------------------------| 8
+ *  |              (8-bit)              |              (8-bit)              |
+ *  |          Protocol [0x04]          |              REASON               | b
+ *  |-----------------------------------+-----------------------------------| y
+ *  |   (1)  | (1) | (2) |   (1)  | (3) | (1)  | (1) |    (1)    |   (5)    | t
+ *  | FID_EN |  X  | FID | PRI_EN | PRI | KEEP |  X  | LEARN_DIS |    X     | e
+ *  |-----------------------------------+-----------------------------------| s
+ *  |   (1)  |                       (15-bit)                               | |
+ *  |  ALLOW |                        TX/RX                                 | v
+ *  |-----------------------------------+-----------------------------------|---
+ *
+ * With the following field descriptions:
+ *
+ *    field      | description
+ *   ------------+-------------
+ *    Realtek    | 0x8899: indicates that this is a proprietary Realtek tag;
+ *     EtherType |         note that Realtek uses the same EtherType for
+ *               |         other incompatible tag formats (e.g. tag_rtl4_a.c)
+ *    Protocol   | 0x04: indicates that this tag conforms to this format
+ *    X          | reserved
+ *   ------------+-------------
+ *    REASON     | reason for forwarding packet to CPU
+ *               | 0: packet was forwarded or flooded to CPU
+ *               | 80: packet was trapped to CPU
+ *    FID_EN     | 1: packet has an FID
+ *               | 0: no FID
+ *    FID        | FID of packet (if FID_EN=1)
+ *    PRI_EN     | 1: force priority of packet
+ *               | 0: don't force priority
+ *    PRI        | priority of packet (if PRI_EN=1)
+ *    KEEP       | preserve packet VLAN tag format
+ *    LEARN_DIS  | don't learn the source MAC address of the packet
+ *    ALLOW      | 1: treat TX/RX field as an allowance port mask, meaning the
+ *               |    packet may only be forwarded to ports specified in the
+ *               |    mask
+ *               | 0: no allowance port mask, TX/RX field is the forwarding
+ *               |    port mask
+ *    TX/RX      | TX (switch->CPU): port number the packet was received on
+ *               | RX (CPU->switch): forwarding port mask (if ALLOW=0)
+ *               |                   allowance port mask (if ALLOW=1)
+ */
+
+#include <linux/bits.h>
+#include <linux/etherdevice.h>
+
+#include "dsa_priv.h"
+
+/* Protocols supported:
+ *
+ * 0x04 = RTL8365MB DSA protocol
+ */
+
+#define RTL8_4_TAG_LEN			8
+
+#define RTL8_4_PROTOCOL			GENMASK(15, 8)
+#define   RTL8_4_PROTOCOL_RTL8365MB	0x04
+#define RTL8_4_REASON			GENMASK(7, 0)
+#define   RTL8_4_REASON_FORWARD		0
+#define   RTL8_4_REASON_TRAP		80
+
+#define RTL8_4_LEARN_DIS		BIT(5)
+
+#define RTL8_4_TX			GENMASK(3, 0)
+#define RTL8_4_RX			GENMASK(10, 0)
+
+static struct sk_buff *rtl8_4_tag_xmit(struct sk_buff *skb,
+				       struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_slave_to_port(dev);
+	__be16 *tag;
+
+	/* Pad out so the (stripped) packet is at least 64 bytes long
+	 * (including FCS), otherwise the switch will drop the packet.
+	 * Then we need an additional 8 bytes for the Realtek tag.
+	 */
+	if (unlikely(__skb_put_padto(skb, ETH_ZLEN + RTL8_4_TAG_LEN, false)))
+		return NULL;
+
+	skb_push(skb, RTL8_4_TAG_LEN);
+
+	dsa_alloc_etype_header(skb, RTL8_4_TAG_LEN);
+	tag = dsa_etype_header_pos_tx(skb);
+
+	/* Set Realtek EtherType */
+	tag[0] = htons(ETH_P_REALTEK);
+
+	/* Set Protocol; zero REASON */
+	tag[1] = htons(FIELD_PREP(RTL8_4_PROTOCOL, RTL8_4_PROTOCOL_RTL8365MB));
+
+	/* Zero FID_EN, FID, PRI_EN, PRI, KEEP; set LEARN_DIS */
+	tag[2] = htons(FIELD_PREP(RTL8_4_LEARN_DIS, 1));
+
+	/* Zero ALLOW; set RX (CPU->switch) forwarding port mask */
+	tag[3] = htons(FIELD_PREP(RTL8_4_RX, BIT(dp->index)));
+
+	return skb;
+}
+
+static struct sk_buff *rtl8_4_tag_rcv(struct sk_buff *skb,
+				      struct net_device *dev)
+{
+	__be16 *tag;
+	u16 etype;
+	u8 reason;
+	u8 proto;
+	u8 port;
+
+	if (unlikely(!pskb_may_pull(skb, RTL8_4_TAG_LEN)))
+		return NULL;
+
+	tag = dsa_etype_header_pos_rx(skb);
+
+	/* Parse Realtek EtherType */
+	etype = ntohs(tag[0]);
+	if (unlikely(etype != ETH_P_REALTEK)) {
+		dev_warn_ratelimited(&dev->dev,
+				     "non-realtek ethertype 0x%04x\n", etype);
+		return NULL;
+	}
+
+	/* Parse Protocol */
+	proto = FIELD_GET(RTL8_4_PROTOCOL, ntohs(tag[1]));
+	if (unlikely(proto != RTL8_4_PROTOCOL_RTL8365MB)) {
+		dev_warn_ratelimited(&dev->dev,
+				     "unknown realtek protocol 0x%02x\n",
+				     proto);
+		return NULL;
+	}
+
+	/* Parse REASON */
+	reason = FIELD_GET(RTL8_4_REASON, ntohs(tag[1]));
+
+	/* Parse TX (switch->CPU) */
+	port = FIELD_GET(RTL8_4_TX, ntohs(tag[3]));
+	skb->dev = dsa_master_find_slave(dev, 0, port);
+	if (!skb->dev) {
+		dev_warn_ratelimited(&dev->dev,
+				     "could not find slave for port %d\n",
+				     port);
+		return NULL;
+	}
+
+	/* Remove tag and recalculate checksum */
+	skb_pull_rcsum(skb, RTL8_4_TAG_LEN);
+
+	dsa_strip_etype_header(skb, RTL8_4_TAG_LEN);
+
+	if (reason != RTL8_4_REASON_TRAP)
+		dsa_default_offload_fwd_mark(skb);
+
+	return skb;
+}
+
+static const struct dsa_device_ops rtl8_4_netdev_ops = {
+	.name = "rtl8_4",
+	.proto = DSA_TAG_PROTO_RTL8_4,
+	.xmit = rtl8_4_tag_xmit,
+	.rcv = rtl8_4_tag_rcv,
+	.needed_headroom = RTL8_4_TAG_LEN,
+};
+module_dsa_tag_driver(rtl8_4_netdev_ops);
+
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL8_4);