[235] in linux-net channel archive
Re: Packet-length patch to lance.c in 1.2.5?
daemon@ATHENA.MIT.EDU (Russell Nelson)
Thu Apr 27 01:55:18 1995
Date: Wed, 26 Apr 95 23:54 EST
From: nelson@crynwr.com (Russell Nelson)
To: linux-net@vger.rutgers.edu
In-reply-to: <9504261735.AA18422@rhett.3do.com> (dplatt@3do.com)
Date: Wed, 26 Apr 95 10:35:06 PDT
From: dplatt@3do.com (Dave Platt)
> Maybe the FCS is stripped by code in *your* changes in 1.2.6, but in
> the 1.2.1 version, it's still there.
Aha! A light dawns. I'll bet you have an original Lance chip (7990 or
79C90).
No, this is a PC-Net/ISA, 79C960.
The older Lance chips don't pad packets out to minimum length, or have
the ability to strip the pad and FCS during reception. The lance.c driver
deals with this difference-in-functionality during transmit - it has some
code to pad out the packets if it sees that an original-era Lance chip
is being used.
Right, agreed, it does that.
The driver does not have (and I don't think it ever has had) code to deal
with this difference during packet reception. It does set the "strip pad
and FCS" bit in CSR4 during chip initialization, and this works fine if
you happen to have a 79c960 PCnet or any of the other more-recent chips.
This CSR isn't implemented by the 7990/79C90 chips, though, and so FCS
stripping does not occur.
Mmmmm, maybe that's what's supposed to happen, but it doesn't work
that way. The FCS gets included. I don't see where it sets the strip
pad and FCS bit in CSR4, not in 1.2.1.
Here's what I think I should do: I'll send Linus a patch against 1.2.6
which will hybridize our changes. I'll either add a new flag to the
chip-type-specific flags (MUST STRIP) or convince myself that it's safe and
proper to overload one of the existing ones (probably MUST PAD). The
skbuff allocator will check this flag, and will perform your four-byte
size reduction if the MUST STRIP flag is set (which will be true for the
Lance and C-Lance, and false for the PCnet).
Seem fair, right, and proper to you?
Only if it works! :)
--
-russ <nelson@crynwr.com> http://www.crynwr.com/~nelson
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