netdev - Waiting for the PHY to complete auto-negotiation

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Date:   Wed, 6 Dec 2017 17:39:00 +0100
From:   Mason <slash.tmp@...e.fr>
To:     netdev <netdev@...r.kernel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        David Miller <davem@...emloft.net>
Subject: Waiting for the PHY to complete auto-negotiation

Hello,

I've been trying to wrap my head around Ethernet auto-negotiation,
vs actual / real packets seen at the MAC layer. I found the relevant
Wikipedia article to be fairly informative:

    https://en.wikipedia.org/wiki/Autonegotiation

The reason I care is that my Ethernet HW does not allow changing the
flow control setting once the MAC has started (more specifically, once
RX DMA has been enabled).

In nb8800_open(), the code currently works in this order:

	nb8800_start_rx(dev);
	phy_start(phydev);

The first line enables the MAC (and DMA).
The second enables the PHY and starts auto-negotiation.

This is a problem: I would like for PHY auto-negotiation to be
/complete/ before I enable the MAC.

What is the recommended way to wait for the PHY?

AFAICT, the PHY layer calls back into the eth driver through the
adjust_link() callback registered through of_phy_connect().
It seems like this might be a good place to enable the MAC?
(When some other conditions are true.)

Regards.