netdev - Re: [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

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Date:   Fri, 30 Nov 2018 23:45:13 +1000
From:   Greg Ungerer <gerg@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     sean.wang@...iatek.com, vivien.didelot@...oirfairelinux.com,
        f.fainelli@...il.com, netdev@...r.kernel.org, blogic@...nwrt.org,
        neil@...wn.name
Subject: Re: [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

Hi Andrew,

On 30/11/18 11:37 pm, Andrew Lunn wrote:
>> 1. TX packets are not getting an IP header checksum via the normal
>>     off-loaded checksumming when in DSA mode. I have to switch off
>>     NETIF_F_IP_CSUM, so the software stack generates the checksum.
>>     That checksum offloading works ok when not using the 7530 DSA driver.
> 
> With some vendors MAC hardware, there is a field in the descriptor to
> indicate how big a VLAN tag the frame has. The hardware can then use
> this information to skip over the VLAN tags to find the IP header, and
> then perform checksuming. You might be able to re-use that, consider
> the DSA header as part of the VLAN header.
> 
> Other vendors, there is no way i've found to get hadware offload of
> checksumming working.

Thanks for the tips, I will try out the master mtu change too.

Regards
Greg