netdev - Re: stmmac: zero udp checksum

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Date:   Mon, 5 Apr 2021 21:30:51 +0200
From:   Julian Labus <julian@...ifunk-rtk.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, mschiffer@...verse-factory.net
Subject: Re: stmmac: zero udp checksum

On 05.04.21 18:42, Andrew Lunn wrote:
> Have you looked at where it actually drops the packet?
> Is it one of
> 
> https://elixir.bootlin.com/linux/latest/source/drivers/net/ethernet/stmicro/stmmac/norm_desc.c#L95
> 
> or
> 
> https://elixir.bootlin.com/linux/latest/source/drivers/net/ethernet/stmicro/stmmac/enh_desc.c#L87
> 
> It could be, you need to see if the checksum has fail, then check if
> the checksum is actually zero, and then go deeper into the frame and
> check if it is a vxlan frame. It could be the linux software checksum
> code knows about this vxlan exception, so you can just run that before
> deciding to drop the frame.
> 
> 	Andrew

No, I've not yet checked where the packet is actually dropped. This is 
my first time debugging a network problem in the kernel and I have 
little to no knowledge how this rx offloading works. But I don't think 
it happens in norm_desc.c#L95 as I would expect the ipc_csum_error 
counter to increase. But the only counters in "ethtool -S" which are 
increasing are mmc_rx_udp_err and mmc_rx_udp_err_octets. I'll try to get 
more information.

Julian