netdev - Re: [PATCH] gianfar: Fix half-duplex operation for non-MII/RMII interfaces

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Message-Id: <ED58F994-6BDC-4496-8445-EA1D984F1379@freescale.com>
Date:	Wed, 24 Jun 2009 15:18:59 -0500
From:	Andy Fleming <afleming@...escale.com>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	David Miller <davem@...emloft.net>,
	Kumar Gala <galak@...nel.crashing.org>,
	Li Yang <leoli@...escale.com>, linuxppc-dev@...abs.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] gianfar: Fix half-duplex operation for non-MII/RMII interfaces


On Jun 24, 2009, at 1:27 PM, Anton Vorontsov wrote:

> It appears that gianfar driver has the same problem[1] that I
> just fixed for ucc_geth.
>
> NFS boot using 10/half link takes about 10 minutes to complete:
>

>
> The symptoms were observed on MPC8379E-RDB boards (eTSEC). Although
> I didn't find where documentation forbids clearing Full Duplex bit
> for non-MII/RMII modes, it's pretty distinct that the bit should be
> set.
>
> It's no wonder though, QE Ethernet and TSEC are pretty similar.

> -			if (!(phydev->duplex))
> -				tempval &= ~(MACCFG2_FULL_DUPLEX);
> +			if (!phydev->duplex &&
> +					(phyi == PHY_INTERFACE_MODE_MII ||
> +					 phyi == PHY_INTERFACE_MODE_RMII))


Hmm....have you tested this on a GMII interface?  *Technically*, full  
duplex is required for GMII, as GMII is used only for gigabit.   
However, we've been treating the GMII interface type as an indicator  
that the PHY *has* a GMII connection to the NIC.  When gianfar detects  
the speed is 10/100 it switches to the compatible MII interface via  
this code, just below:

                         case 100:
                         case 10:
                                 tempval =
                                     ((tempval & ~(MACCFG2_IF)) |  
MACCFG2_MII);


My concern is that you will be detecting the GMII interface, and  
disallowing half-duplex, despite the fact that the interface is  
actually running at 10 or 100 Mbit.

Andy
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