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:

quoted

On Wed, Nov 07, 2018 at 08:41:52PM +0100, Heiner Kallweit wrote:

quoted

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. 

quoted

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