linux-kernel - Re: [PATCH 1/2] of_mdio: add new DT property 'link' for fixed-link

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Message-ID: <55A00D7C.9090807@gmail.com>
Date:	Fri, 10 Jul 2015 11:22:52 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Stas Sergeev <stsp@...t.ru>, Sebastien Rannou <mxs@...k.org>
CC:	Linux kernel <linux-kernel@...r.kernel.org>,
	Arnaud Ebalard <arno@...isbad.org>,
	Stas Sergeev <stsp@...rs.sourceforge.net>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	devicetree@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH 1/2] of_mdio: add new DT property 'link' for fixed-link

On 10/07/15 04:20, Stas Sergeev wrote:
> 10.07.2015 11:46, Sebastien Rannou пишет:
>> On Fri, 10 Jul 2015, Stas Sergeev wrote:
>>
>>> 10.07.2015 00:15, Florian Fainelli пишет:
>>>> Then, if the in-band status indication is not reliable (which really
>>>> should be completely understood),
>>> Agree!
>>> But this is not something I can help with.
>>> Sebastien Rannou reports the problem, please ask him whatever
>>> you see fits to get a better understanding of a problem.
>>> The fact that his HW does not generate the inband status, is
>>> _my own guess_.
>>
>> Yes, I confirm that my HW does not generate an in-band status. AFAIK, it's
>> a PHY that aggregates 4xSGMIIs to 1xQSGMII ; the MAC side of the PHY (with
>> inband status) is connected to the switch through QSGMII, and in this context
>> we are on the media side of the PHY.
> Hmm, interesting.
> So if I parse the above correctly, you have something like 88E1340S set
> up into a mode when SGMII is used as media interface and QSGMII as system
> interface (terms are from datasheet page 5), then you connect the media
> interface to armada-xp and system interface to the switch.
> 
> I wonder if it is the right thing to do.
> AFAIK you could as well set up armada-xp into QSGMII mode and connect
> that to switch. The driver would then disable the use of inband status
> and everything would be fine.
> Either way, your use-case proves that only DT can decide the use of an
> inband status.

I do not think there is any debate around the need for a property that
defines whether in-band-status is both reliable and usable, the debate
is about *where* to put it.

I still think this does not belong in the fixed-link property, but now
that you have explained a bit more in the other patch what your
understanding of "fixed-link" is, I can see the confusion.

Instead of having a link = "auto", property, how about just something
like this:

fixed-link {
	speed = <1000>;
	full-duplex;
	use-in-band-status;
};

or event this:

fixed-link {
	use-in-band-status;
};

If you parse the 'use-in-band-status' which means that it is reliable
information, then you can override whatever was defined in the DT under
the 'fixed-link' property?
-- 
Florian
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