linux-kernel - Re: [PATCH 2/3] of_mdio: add new DT property 'autoneg' for fixed-link

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Date:	Sat, 11 Jul 2015 00:02:45 +0300
From:	Stas Sergeev <stsp@...t.ru>
To:	Florian Fainelli <f.fainelli@...il.com>,
	netdev <netdev@...r.kernel.org>
Cc:	Linux kernel <linux-kernel@...r.kernel.org>,
	Sebastien Rannou <mxs@...k.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" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/3] of_mdio: add new DT property 'autoneg' for fixed-link

10.07.2015 23:39, Florian Fainelli пишет:
>> - in-band status is an implementation delail, and it is
>> specific to a particular protocols. If you request the
>> in-band status for some protocol that doesn't support
>> it, perhaps you should get -EINVAL, because such a
>> config makes no sense. With autonegotiation, the rules
>> are not that strict: it can be "unimplemented", which doesn't
>> necessary mean nonsense in the config.
> So by specifying "autoneg", you are not specific about the kind of
> auto-negotiation protocol available, which is precisely my point: you
> need to go down to that level of detail for this to be useful. So maybe
> something like:
>
> autoneg = "in-band-status" would actually be a better thing in terms of
> description because then you would tell what can be made available/working?
I would agree with this if your argument below is true (see below).

>> - autonegotiation is a wider term, and may be implemented
>> by some other means than the in-band status (which is
>> probably impossible for a fixed-link though).
>>
>> - In the terms that the driver uses, it is autonegotiation, eg
>> MVNETA_GMAC_AUTONEG_CONFIG. And when you go down
>> the implementation details, you see MVNETA_GMAC_INBAND_AN_ENABLE,
>> which is just one AN bit of many.
> But arguably, there could be another auto-negotiation method, which is
> not in-band status related, which means that you would need a way to
> distinguish between using in-band status, or using something else or
> nothing, would not you?
"something else" is a big question here.
Can you think of _any_ other way that is both not an MDIO
(suits to fixed-link) and not an in-band?
If the answer is yes (even theoretically), then
autoneg = "in-band" | "off"
may make sense. Otherwise boolean just looks enough.
If we would implement autoneg outside of the fixed-link,
then its semantic would likely be
autoneg = "mdio" | "in-band" | "off"
But the fact that we put it under fixed-link where only a
single AN possibility exist, may probably be underlined by
a semantic specific to fixed-link.

One may also argue that
autoneg = "any-possible-autoneg-that-works" is better than
specifying it explicitly, which is exactly what the boolean does.
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