Re: [PATCHv10 08/12] mlx4: Add support for IBoE - address resolution

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > I don't get this. For IB, we have 72 without immediate - did you
 > forget to add the ICRC? I think we count it with the header...

We don't need ICRC in the header_buf, do we?  We're talking about
MLX4_IB_UD_HEADER_SIZE, which is used to hold the packet header we get
from ib_ud_header_pack().  The ICRC is accounted for in a different
segment of the WQE.

In any case, it shouldn't matter -- I don't see how it could be correct
to increase the buffer size by 4 bytes to account for the change from
LRH to Ethernet header; an LRH is 8 bytes and an Ethernet header
(without .1q etc) is 14 bytes.  So we should add 6 bytes, right?

The math I get is

IB:   LRH + GRH + BTH + DETH + IMM
       8    40    12     8      4   = 72

Eth:  MAC + GRH + BTH + DETH + IMM
      14    40    12     8      4   = 78

I don't see how your change

 > -	MLX4_IB_UD_HEADER_SIZE		= 72,
 > +	MLX4_IB_UD_HEADER_SIZE		= 76,

could possibly be correct, although as I said it probably works because
of padding and not hitting the worst case in practice anyway.

 - R.

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