Re: [PATCH net-next 08/13] net: dsa: hellcreek: deny tc-taprio changes to per-tc max SDU

On Wed Sep 21 2022, Vladimir Oltean wrote:

On Wed, Sep 21, 2022 at 01:23:24PM +0200, Kurt Kanzenbach wrote:

quoted

On Thu Sep 15 2022, Vladimir Oltean wrote:

quoted

On Thu, Sep 15, 2022 at 08:15:54AM +0200, Kurt Kanzenbach wrote:

quoted

quoted

So the maxSDU hardware register tracks exactly the L2 payload size, like
the software variable does, or does it include the Ethernet header size
and/or FCS?

This is something I'm not sure about. I'll ask the HW engineer when he's
back from vacation.

You can also probably figure this out by limiting the max-sdu to a value
like 200 and seeing what frame sizes pass through.

So, configured to 128 and 132 bytes (including VLAN Ethernet header) is
the maximum frame size which passes through.

Frame size means MAC DA + MAC SA + VLAN header + Ethertype + L2 payload,
and without FCS, right?

Yes.

Because max_sdu 128 only counts the L2 payload, so the maximum frame
size that passes should be 142 octets, or 146 octets with VLAN.

Ok, i see. So, for 128 max-sdu we should end up with something like this
in the prio config register:

 schedule->max_sdu[tc] + VLAN_ETH_HLEN - 4

Thanks,
Kurt