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Re: [PATCH 1/2] netdev: octeon_mgmt: Correct tx IFG workaround.

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [PATCH 1/2] netdev: octeon_mgmt: Correct tx IFG workaround.
From: Joe Perches <joe@perches.com>
Date: Wed, 19 Jun 2013 18:37:19 -0700
Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>, linux-mips@linux-mips.org, David Daney <david.daney@cavium.com>
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On Wed, 2013-06-19 at 18:28 -0700, David Daney wrote:
> On 06/19/2013 06:08 PM, Joe Perches wrote:
> > On Wed, 2013-06-19 at 17:40 -0700, David Daney wrote:
> >> From: David Daney <david.daney@cavium.com>
> >>
> >> The previous fix was still too agressive to meet ieee specs.  Increase
> >> to (14, 10).
> > []
> >> diff --git a/drivers/net/ethernet/octeon/octeon_mgmt.c 
> >> b/drivers/net/ethernet/octeon/octeon_mgmt.c
> > []
> >> @@ -1141,10 +1141,13 @@ static int octeon_mgmt_open(struct net_device 
> >> *netdev)
> >>            /* For compensation state to lock. */
> >>            ndelay(1040 * NS_PER_PHY_CLK);
> >>
> >> -          /* Some Ethernet switches cannot handle standard
> >> -           * Interframe Gap, increase to 16 bytes.
> >> +          /* Default Interframe Gaps are too small.  Recommended
> >> +           * workaround is.
> >> +           *
> >> +           * AGL_GMX_TX_IFG[IFG1]=14
> >> +           * AGL_GMX_TX_IFG[IFG2]=10
> >
> > Why isn't the TX IFG just 96 bit times?
> 
> I don't have a full understanding of how the transistors are wired up on 
> the chip, so I cannot accurately answer your question.  But I can say 
> that after I empirically found the previous values to get the thing to 
> work, the hardware designers independently found that the values 
> supplied in this patch are required to achieve industry standard IFGs 
> with this hardware.

For one specific chip or for the Octeon entire family?



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