netdev - Re: [PATCH v5 net-next] net: ftmac100: support mtu

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Date:   Thu, 27 Oct 2022 10:31:39 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Sergei Antonov <saproj@...il.com>, netdev@...r.kernel.org
Cc:     olteanv@...il.com, andrew@...n.ch, kuba@...nel.org,
        edumazet@...gle.com, davem@...emloft.net
Subject: Re: [PATCH v5 net-next] net: ftmac100: support mtu > 1500

Hello,

On Mon, 2022-10-24 at 20:58 +0300, Sergei Antonov wrote:
> The ftmac100 controller considers packets >1518 (1500 + Ethernet + FCS)
> FTL (frame too long) and drops them. That is fine with mtu 1500 or less
> and it saves CPU time. When DSA is present, mtu is bigger (for VLAN
> tagging) and the controller's built-in behavior is not desired then. We
> can make the controller deliver FTL packets to the driver by setting
> FTMAC100_MACCR_RX_FTL. Then we have to check ftmac100_rxdes_frame_length()
> (packet length sans FCS) on packets marked with FTMAC100_RXDES0_FTL flag.
> 
> Check for mtu > 1500 in .ndo_open() and set FTMAC100_MACCR_RX_FTL to let
> the driver FTL packets. Implement .ndo_change_mtu() and check for
> mtu > 1500 to set/clear FTMAC100_MACCR_RX_FTL dynamically.
> 
> Fixes: 8d77c036b57c ("net: add Faraday FTMAC100 10/100 Ethernet driver")

For the records, Vladimir explicitly asked you to drop the 'Fixes' tag.
Such tag makes little sense for a net-next commit, especially when
referring to an old change - e.g. that did not enter mainline in this
release cycle.

Cheers,

Paolo