netdev - Re: Phy read timeout in ibm_new

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Message-Id: <1208347791.6958.279.camel@pasglop>
Date:	Wed, 16 Apr 2008 22:09:51 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	M B <super.firetwister@...glemail.com>
Cc:	netdev@...r.kernel.org, ppc-dev <linuxppc-dev@...abs.org>
Subject: Re: Phy read timeout in ibm_new_emac driver


> My Micrel/Kendin KSZ8721BT on my ppc405EP board needs one us longer to
> finish. I was able to reproduce this all the time. So I wonder if the
> timeout of 100us is defined by the MII standard, or by the author of
> the driver?
> If it's a standard I've still a bad feeling if we just correct the
> timeout to 100us, maybe 110 should be fine. If it's not defined by the
> standard, I would add 50% to the timeout. It won't slow down other
> phys, but a scan on the phy bus might get slowed down.
> Same applies for __emac_mdio_write.
> 
> Oh and we could save a us by putting the udelay(1) after the if section ;-)

Increasing the timeout is fine. In fact, EMAC specifically can sleep in
it's MDIO access routines (it already takes mutexes) so maybe a good
option here is to use longer sleeping delays and less iterations.

Somebody knows off hand what the standard says the timeout should be ? I
can check that tomorrow, I don't have it at hand right now and it's
getting late but feel free to beat me to it :-) 

Cheers,
Ben.

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