linux-kernel - Re: [PATCH net-next 4/6] net: dsa: tag_rtl8

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Date:   Wed, 13 Oct 2021 13:02:02 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Alvin Šipraga <alvin@...s.dk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        netdev <netdev@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 4/6] net: dsa: tag_rtl8_4: add realtek 8 byte
 protocol 4 tag

On Tue, Oct 12, 2021 at 2:37 PM Alvin Šipraga <alvin@...s.dk> wrote:

> From: Alvin Šipraga <alsi@...g-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@...g-olufsen.dk>

The code definately looks good:
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Some nitpicky personal preferences below:

> +#define RTL8_4_TAG_LEN                 8
> +/* 0x04 = RTL8365MB DSA protocol
> + */
> +#define RTL8_4_PROTOCOL_RTL8365MB      0x04

This is #defined

> +       /* Zero FID_EN, FID, PRI_EN, PRI, KEEP; set LEARN_DIS */
> +       tag[2] = htons(1 << 5);

I would create defines for the flags like this:
#define RTL8365MB_LEARN_DIS BIT(5)

> +       /* Parse Protocol */
> +       proto = ntohs(tag[1]) >> 8;

In the 4byte header code we have something like this:
#define RTL8_4_PROTOCOL_SHIFT 8

> +       /* Parse TX (switch->CPU) */
> +       port = ntohs(tag[3]) & 0xf; /* Port number is the LSB 4 bits */

This I think is fair enough. No need to define that mask.

Yours,
Linus Walleij