linux-kernel - Re: [PATCH net-next] mvpp2: document HW checksum behaviour

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Date:   Sun, 28 Jul 2019 16:30:40 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Antoine Tenart <antoine.tenart@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next] mvpp2: document HW checksum behaviour

On Sun, Jul 28, 2019 at 3:36 AM Matteo Croce <mcroce@...hat.com> wrote:
>
> On Fri, Jul 26, 2019 at 2:57 PM Antoine Tenart
> <antoine.tenart@...tlin.com> wrote:
> >
> > Hi Matteo,
> >
> > On Fri, Jul 26, 2019 at 01:15:46AM +0200, Matteo Croce wrote:
> > > The hardware can only offload checksum calculation on first port
> > > due to the Tx FIFO size limitation. Document this in a comment.
> > >
> > > Fixes: 576193f2d579 ("net: mvpp2: jumbo frames support")
> > > Signed-off-by: Matteo Croce <mcroce@...hat.com>
> >
> > Looks good. Please note there's a similar code path in the probe.
> > You could also add a comment there (or move this check/comment in a
> > common place).
> >
> > Thanks!
> > Antoine
> >
>
> Hi Antoine,
>
> I was making a v2, when I looked at the mvpp2_port_probe() which does:
>
> --------------------------------%<------------------------------
> features = NETIF_F_SG | NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
> NETIF_F_TSO;
>
> if (port->pool_long->id == MVPP2_BM_JUMBO && port->id != 0) {
>     dev->features &= ~(NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM);
>     dev->hw_features &= ~(NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM);
> }
>
> dev->vlan_features |= features;
> -------------------------------->%------------------------------
>
> Is it ok to remove NETIF_F_IP*_CSUM from dev->features and
> dev->hw_features but keep it in dev->vlan_features?
>
> Regards,
> --
> Matteo Croce
> per aspera ad upstream

Hi all,

probably dev->vlan_features is safe to keep the CSUM features to avoid
unnecessary calculation in some cases, but I have another question.
Does the PP2 hardware support checksumming within any offset? I
replaced 'NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM' with NETIF_F_HW_CSUM and
then stacked 5 VxLANS on top of a mvpp2 device, to have the last IP
header at offset 264:

ip link set $dev up
ip addr add 192.168.0.$last/24 dev $dev

for i in {1..5}; do
	ip link add vx$i type vxlan id $i dstport 4789 remote 192.168.$((i-1)).$other
	ip link set vx$i up
	ip addr add 192.168.$i.$last/24 dev vx$i
done

00:51:82:11:22:00 > 3c:fd:fe:9c:60:6c, ethertype IPv4 (0x0800), length 348: 192.168.0.1.33625 > 192.168.0.2.4789: VXLAN, flags [I] (0x08), vni 1
02:25:60:da:87:03 > 92:20:05:45:3d:d3, ethertype IPv4 (0x0800), length 298: 192.168.1.1.33625 > 192.168.1.2.4789: VXLAN, flags [I] (0x08), vni 2
12:20:97:15:8f:aa > 66:08:23:c7:72:ea, ethertype IPv4 (0x0800), length 248: 192.168.2.1.33625 > 192.168.2.2.4789: VXLAN, flags [I] (0x08), vni 3
c6:1c:b9:fd:9d:28 > 22:ca:cb:6a:ea:68, ethertype IPv4 (0x0800), length 198: 192.168.3.1.33625 > 192.168.3.2.4789: VXLAN, flags [I] (0x08), vni 4
02:34:5f:45:a5:9d > d2:4e:d4:d7:42:31, ethertype IPv4 (0x0800), length 148: 192.168.4.1.34504 > 192.168.4.2.4789: VXLAN, flags [I] (0x08), vni 5
a2:99:fd:9c:1b:05 > 5a:81:3b:fc:6a:07, ethertype IPv4 (0x0800), length 98: 192.168.5.1 > 192.168.5.2: ICMP echo request, id 1654, seq 156, length 64

It seems that the HW is capable of doing it, can someone with a
datasheet confirm this?

Regards,
-- 
Matteo Croce
per aspera ad upstream