From: Scott Feldman <sfeldma@pobox.com>
Date: Wed, 9 Nov 2005 07:18:52 +0000 (-0500)
Subject: [netdrvr e100] experiment with doing RX in a similar manner to eepro100
X-Git-Tag: v2.6.22-rc1~1110^2~18
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d52df4a35af569071fda3f4eb08e47cc7023f094;p=pandora-kernel.git

[netdrvr e100] experiment with doing RX in a similar manner to eepro100

I was going to say that eepro100's speedo_rx_link() does the same DMA
abuse as e100, but then I noticed one little detail: eepro100 sets  both
EL (end of list) and S (suspend) bits in the RFD as it chains it  to the
RFD list.  e100 was only setting the EL bit.  Hmmm, that's  interesting.
That means that if HW reads a RFD with the S-bit set,  it'll process
that RFD and then suspend the receive unit.  The  receive unit will
resume when SW clears the S-bit.  There is no need  for SW to restart
the receive unit.  Which means a lot of the receive  unit state tracking
code in the driver goes away.

So here's a patch against 2.6.14.  (Sorry for inlining it; the mailer
I'm using now will mess with the word wrap).  I can't test this on
XScale (unless someone has an e100 module for Gumstix :) .  It should
be doing exactly what eepro100 does with RFDs.  I don't believe this
change will introduce a performance hit because the S-bit and EL-bit  go
hand-in-hand meaning if we're going to suspend because of the S- bit,
we're on the last resource anyway, so we'll have to wait for SW  to
replenish.
(cherry picked from 29e79da9495261119e3b2e4e7c72507348e75976 commit)
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