netdev - Re: net/fec: Unable to get a permanent link when connecting to a PC

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Date:	Mon, 22 Sep 2014 10:06:14 +0200
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	"to-fleischer@...nline.de" <to-fleischer@...nline.de>,
	linux-arm-kernel@...ts.infradead.org,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: net/fec: Unable to get a permanent link when connecting to a
 PC

Am 19.09.2014 um 11:33 schrieb to-fleischer@...nline.de:
> I have an i.MX283 board with a KSZ8081 PHY that is connected to the controller
> via RMII. The PHY's interrupt line is currently unused, but connected to the
> controller. The board runs the linux version 3.17-rc5.
> When I connect the board directly to a PC the ethernet link goes up and a second
> later down. This is repeated again and again.
> After some investigation I found that this is caused by the reset of the FEC at
> the begin of fec_restart() that is called by fec_enet_adjust_link() if the link
> is up.
> Due to the reset the mode is set to MII. After switching back to RMII the PHY 
> seems to restart the autonegotiation. Since this takes a while the next call of 
> phy_state_machine() detects that the link is down.
> It would work, if the reset in fec_restart is avoided for the case that the link
> goes up and the fec is still stopped.
>
> Its quite remarkable that this issue does not occur if I connect the board to a
> switch or if I use the PHY's interrupt line.
>
> What do you think?
>
> Best Regards,
> Torsten Fleischer
>

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Best regards
Stefan Wahren
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