Question about dev.fxp.0.noflow

[Andrey Chernov]

On Thu, Dec 20, 2007 at 10:25:22AM +0900, Pyun YongHyeon wrote:
> On Wed, Dec 19, 2007 at 04:33:44AM +0300, Andrey Chernov wrote:
>  > Does anybody know why dev.fxp.0.noflow=1 by default?
>  > Is it more proper to set it to 0? (by default or via /etc/sysctl.conf)
>  > 
> 
> Since flow control is valid only when link partner also agrees on
> advertised pause capability on full-duplex media, it needs more work
> in mii/phy driver to advertise correct pause capability. It also needs
> a way to pass negotiated pause capability back to drvier such that
> each drvier should program necessary flow control parameters depending
> on its MAC capability and negociated ones. Just enabling flow control
> on one side have no effect.

I also found this note in the commit log:

date: 2003/05/16 01:13:16;  author: rwatson;  state: Exp;  lines: +5 -1
Add a tunable/sysctl "hw.fxp_noflow" which disables flow control support
on if_fxp cards.  When flow control is enabled, if the operating system
doesn't acknowledge the packet buffer filling, the card will begin to
generate ethernet quench packets, but appears to get into a feedback
loop of some sort, hosing local switches.  This is a temporary workaround
for 5.1: the ability to configure flow control should probably be
exposed by some or another management interface on ethernet link layer
devices.

Does it mean card hardware defect or lack of driver support? I.e. is this 
phrase 
"When flow control is enabled, if the operating system doesn't acknowledge 
the packet buffer filling"
still true with latest drivers framework (the note as old as 2003)?

-- 
http://ache.pp.ru/