netdev - Re: Freescale FEC packet loss

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Message-ID: <CAH9NwWeK17kfty-BAA9Y977BGTYBcJLRSRESrfbCvQ_BiVxa0A@mail.gmail.com>
Date:	Thu, 6 Feb 2014 10:42:00 +0100
From:	Christian Gmeiner <christian.gmeiner@...il.com>
To:	Marek Vasut <marex@...x.de>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Frank Li <Frank.Li@...escale.com>, Detlev Zundel <dzu@...x.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Eric Nelson <eric.nelson@...ndarydevices.com>,
	Hector Palacios <hector.palacios@...i.com>,
	fugang.duan@...escale.com,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Freescale FEC packet loss

2014-01-28 Marek Vasut <marex@...x.de>:
> On Sunday, January 26, 2014 at 10:33:33 PM, Ben Hutchings wrote:
>> On Sun, 2014-01-26 at 20:12 +0100, Marek Vasut wrote:
>> > On Sunday, January 26, 2014 at 07:56:30 PM, Ben Hutchings wrote:
>> > > On Wed, 2014-01-22 at 22:55 +0100, Marek Vasut wrote:
>> > > > Hi guys,
>> > > >
>> > > > I am running stock Linux 3.13 on i.MX6Q SabreLite board. The CPU is
>> > > > i.MX6Q TO 1.0 .
>> > > >
>> > > > I am hitting a WARNING when I use the FEC ethernet to transfer data,
>> > > > thus I started investigating this problem. TL;DR I am not able to
>> > > > figure this problem out, so I am not attaching a patch :-(
>> > > >
>> > > > Steps to reproduce:
>> > > > -------------------
>> > > > 1) Boot stock Linux 3.13 on i.MX6Q SabreLite board
>> > > > 2) Plug in an SD card into one of the SD slots (I use the full-size
>> > > > one) 3) Plug in an USB stick into one of the USB ports (I use the
>> > > > upper one) 4) Plug in an ethernet cable into the board
>> > > >
>> > > >    -> Connect the other side into a gigabit-capable PC
>> > >
>> > > [...]
>> > >
>> > > I think there are known problems with 1000BASE-T on the Sabre Lite
>> > > board.
>> >
>> > This is MX6-wide thing, not sabrelite specific actually.
>> >
>> > > Two possible workarounds are to limit the PHY to 100BASE-TX
>> > > (should be doable with ethtool) or force it to be clock master for
>> > > 1000BASE-T (requires a driver patch).
>> >
>> > Can you please elaborate on the later ? I don't quite understand that.
>>
>> 1000BASE-T uses all 4 pairs in both directions at the same time, which
>> requires that both ends transmit symbols synchronously.  As part of the
>> autonegotiation protocol, they decide which is the clock master (using a
>> local clock generator) and which is the clock slave (generating a clock
>> from the received signal).  A PHY can be configured to support only one
>> of these roles.
>
> I checked the patch you pointed me to. The patch basically messes with the
> CTL1000 (0x9) register of the PHY, right ? I did the adjustments to the PHY
> register manually , but the result is still the same (backtrace).
>
> I did two different kinds of adjustment:
> 1) reg 0x9 |= 0x1800;
> 2) reg 0x9 |= 0x1000;
> In both cases, the crash did happen. I verified the PHY register was configured
> as necessary. The KSZ9021 PHY bit 12 configures the master/slave override, same
> as the patch does. The bit 11 forces either master or slave mode for the PHY. In
> both cases the crash was there.
>
> I think this patch won't help in this case, sorry.
>

Are there still problems with 3.13.1 kernel regarding FEC networking?
Does this only
affect the SabreLite?

greets
--
Christian Gmeiner, MSc

https://soundcloud.com/christian-gmeiner
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