Messages in this thread | | | Subject | Re: [PATCH 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum | From | Florian Fainelli <> | Date | Thu, 15 Jul 2021 09:24:09 -0700 |
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On 7/15/21 6:08 AM, Andrew Lunn wrote: >> - If we inherit NETIF_F_HW_CSUM from the master for tail taggers, it is >> actively detrimential to keep this feature enabled, as proven my Lino. >> As for header taggers, I fail to see how this would be helpful, since >> the DSA master would always fail to see the real IP header (it has >> been pushed to the right by the DSA tag), and therefore, the DSA >> master offload would be effectively bypassed. > > The Marvell MACs know about DSA and should be able to perform hardware > checksumming. It is a long time since i looked at how this works, but > i think there is a field in the descriptor which gets set with the > offset to the IP header, so it work for DSA as well as EDSA. > > I _think_ Broadcom MACs also know about Broadcom tags and can do the > right thing.
Yes, the SYSTEMPORT MAC as well as bgmac to some extent will automagically work, but they have to be told to expect a Broadcom tag in order to generate an appropriate checksum on receive. This is why we have this:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/broadcom/bcmsysport.c#n144
Likewise, for TX:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/broadcom/bcmsysport.c#n172 -- Florian
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