From: Jesper Dangaard Brouer <redacted>
Date: Thu, 21 Jan 2016 12:27:30 +0100

eth_type_trans() does two things:

1) determine skb->protocol
2) setup skb->pkt_type = PACKET_{BROADCAST,MULTICAST,OTHERHOST}

Could the HW descriptor deliver the "proto", or perhaps just some bits
on the most common proto's?

The skb->pkt_type don't need many bits.  And I bet the HW already have
the information.  The BROADCAST and MULTICAST indication are easy.  The
PACKET_OTHERHOST, can be turned around, by instead set a PACKET_HOST
indication, if the eth->h_dest match the devices dev->dev_addr (else a
SW compare is required).

Is that doable in hardware?

I feel like we've had this discussion before several years ago.

I think having just the protocol value would be enough.

skb->pkt_type we could deal with by using always an accessor and
evaluating it lazily.  Nothing needs it until we hit ip_rcv() or
similar.