netdev - Re: [PATCH net-next 0/5] net: phy: improve and simplify phylib state machine

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Message-ID: <20181107202156.GD9599@lunn.ch>
Date:   Wed, 7 Nov 2018 21:21:56 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 0/5] net: phy: improve and simplify phylib state
 machine

On Wed, Nov 07, 2018 at 09:05:49PM +0100, Heiner Kallweit wrote:
> On 07.11.2018 20:48, Andrew Lunn wrote:
> > On Wed, Nov 07, 2018 at 08:41:52PM +0100, Heiner Kallweit wrote:
> >> This patch series is based on two axioms:
> >>
> >> - During autoneg a PHY always reports the link being down
> > 
> > Hi Heiner
> > 
> > I think that is a risky assumption to make.
> > 
> I wasn't sure initially too (found no clear rule in 802.3 clause 22)
> and therefore asked around. Florian agrees to the assumption,
> see here: https://www.spinics.net/lists/netdev/msg519242.html
> 
> If a PHY reports the link as up then every user would assume that
> data can be transferred. But that's not the case during aneg.
> Therefore reporting the link as up during aneg wouldn't make sense.

Hi Heiner

If auto-neg has already been completed once before, i can see a lazy
hardware designed not reporting link down, or at least, not until
auto-neg actually fails.

And what about if link is down for too short a time for us to notice?
I've seen some code fail because the kernel went off and did something
else for too long, and a state change was missed. 

> > What happens if this assumption is incorrect?
> > 
> Then we have to flush this patch series down the drain ;)
> At least I would have to check in detail which parts need to be
> changed. I clearly mention the assumptions so that every
> reviewer can check whether he agrees.

Thanks for doing that. I want to be happy this is safe, and not going
to introduce regressions.

   Andrew