Re: [RFC PATCH net-next 3/5] net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag

[Alvin Šipraga]

Hi Andrew,

On 8/23/21 12:02 AM, Andrew Lunn wrote:
> On Sun, Aug 22, 2021 at 09:31:41PM +0200, Alvin Šipraga wrote:
>> diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
>> index 548285539752..470a2f3e8f75 100644
>> --- a/net/dsa/Kconfig
>> +++ b/net/dsa/Kconfig
>> @@ -99,6 +99,12 @@ 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.
>> +
> 
> Hi Alvin
> 
> This file is sorted based on the tristate text. As such, the
> NET_DSA_TAG_RTL4_A is in the wrong place. So i can understand why you
> put it here, but place move it after the Qualcom driver.

Thanks - I'll fix it in v2.

> 
>> @@ -11,6 +11,7 @@ obj-$(CONFIG_NET_DSA_TAG_GSWIP) += tag_gswip.o
>>   obj-$(CONFIG_NET_DSA_TAG_HELLCREEK) += tag_hellcreek.o
>>   obj-$(CONFIG_NET_DSA_TAG_KSZ) += tag_ksz.o
>>   obj-$(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_LAN9303) += tag_lan9303.o
>>   obj-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o
>>   obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o
> 
> The CONFIG_NET_DSA_TAG_RTL4_A is also in the wrong place...

Ditto.

> 
>> diff --git a/net/dsa/tag_rtl8_4.c b/net/dsa/tag_rtl8_4.c
>> new file mode 100644
>> index 000000000000..1082bafb6a2e
>> --- /dev/null
>> +++ b/net/dsa/tag_rtl8_4.c
>> @@ -0,0 +1,178 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Handler for Realtek 8 byte switch tags
>> + *
>> + * Copyright (C) 2021 Alvin Šipraga <alsi@xxxxxxxxxxxxxxx>
>> + *
>> + * NOTE: Currently only supports protocol "4" found in the RTL8365MB, hence
>> + * named tag_rtl8_4.
>> + *
>> + * This "proprietary tag" header has the following format:
> 
> I think they are all proprietary. At least, there is no
> standardization across vendors.

I'll remove in v2.

> 
>> + *
>> + *  -------------------------------------------
>> + *  | 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
> 
> Are you allowed to document reason? This could be interesting for some
> of the future work.

Unfortunately the reason field is undocumented. The vendor driver 
doesn't contain any parsing code for the CPU tag so we are left to 
guess. One obvious example would be trapped packets, since the switch 
lets you configure what to do with those (drop, forward to CPU, etc.).

I have not had a reason to look into this yet, otherwise I would have 
documented whatever I knew about it. Hope it's OK for now.

> 
>> + *    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)
> 
> There are some interesting fields here. It will be interesting to see
> what we can do with the switch.

This is exactly why I asked for Realtek's permission to publish the 
details. :-)

> 
>> + */
>> +
>> +#include <linux/etherdevice.h>
>> +#include <linux/bits.h>
>> +
>> +#include "dsa_priv.h"
>> +
>> +#define RTL8_4_TAG_LEN			8
>> +#define RTL8_4_ETHERTYPE		0x8899
> 
> Please add this to include/uapi/linux/if_ether.h

I believe Realtek uses this EtherType for a bunch of unrelated 
protocols, so I'm not sure this is a good idea. See [1] for a similar 
discussion on the mailing list a while back. What do you think?

[1] 
https://lore.kernel.org/netdev/CACRpkdYQthFgjwVzHyK3DeYUOdcYyWmdjDPG=Rf9B3VrJ12Rzg@xxxxxxxxxxxxxx/

> 
>> +static struct sk_buff *rtl8_4_tag_rcv(struct sk_buff *skb,
>> +				      struct net_device *dev)
>> +{
>> +	__be16 *p;
>> +	u16 etype;
>> +	u8 proto;
>> +	u8 *tag;
>> +	u8 port;
>> +	u16 tmp;
>> +
>> +	if (unlikely(!pskb_may_pull(skb, RTL8_4_TAG_LEN)))
>> +		return NULL;
>> +
>> +	tag = dsa_etype_header_pos_rx(skb);
>> +
>> +	/* Parse Realtek EtherType */
>> +	p = (__be16 *)tag;
>> +	etype = ntohs(*p);
>> +	if (unlikely(etype != RTL8_4_ETHERTYPE)) {
>> +		netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
> 
> You probably want to rate limit these sorts of prints. You have
> limited controller of what frames come in, and if somebody can craft
> bad frames, they can make you send all your time printing messages to
> the log.

OK, I think I saw some rate limited version of netdev_dbg so I'll bring 
that in for v2. Thanks for the tip.

> 
>      Andrew
>