netdev - Re: Query on new ethtool RSS hashing options

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Date:   Sat, 06 Mar 2021 22:16:12 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        George Cherian <gcherian@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        Sunil Goutham <sgoutham@...vell.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: Query on new ethtool RSS hashing options

On Sat, Mar 06, 2021 at 14:54, Vladimir Oltean <olteanv@...il.com> wrote:
> On Sat, Mar 06, 2021 at 05:38:14PM +0530, Sunil Kovvuri wrote:
>> > Can you share the format of the DSA tag? Is there a driver for it
>> > upstream? Do we need to represent it in union ethtool_flow_union?
>> >
>> 
>> No, there is no driver for this tag in the kernel.
>> I have attached the tag format.
>> There are multiple DSA tag formats and representing them ethtool_flow
>> union would be difficult.
>> Hence wondering if it would be okay to add a more flexible way ie
>> offset and num_bytes from the start of packet.
>
> How sure are you that the tag format you've shared is not identical to
> the one parsed by net/dsa/tag_dsa.c?

That is indeed the format parsed by tag_dsa.c. Based on the layout in
the image, I am pretty sure that it is from the functional spec. of the
Amethyst (6393X). So while the format is supported, that specific device
is not. Hopefully that will change soon:

https://lore.kernel.org/netdev/cover.1610071984.git.pavana.sharma@digi.com/

As for the NIC: Marvell has an EVK for the Amethyst, connected to a
CN9130 SoC. The ethernet controllers in those can parse DSA tags in
hardware, so I would put my money on that.

The upstream driver (mvpp2) does not seem to support it though, AFAIK.