From: Andrew Lunn <andrew@lunn•ch>
To: Mason <slash.tmp@free•fr>
Cc: netdev <netdev@vger•kernel.org>,
Florian Fainelli <f.fainelli@gmail•com>,
David Miller <davem@davemloft•net>
Subject: Re: Waiting for the PHY to complete auto-negotiation
Date: Wed, 6 Dec 2017 17:59:03 +0100 [thread overview]
Message-ID: <20171206165903.GM27063@lunn.ch> (raw)
In-Reply-To: <e54cda57-6a7d-611e-89b9-0b3c9ea55cc1@free.fr>
On Wed, Dec 06, 2017 at 05:39:00PM +0100, Mason wrote:
> 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?
That probably works, but you might have a few corner cases to handle.
I'm not sure changes at the PHY always transition through down. So you
could for example get a callback saying the link is up, 1Gbps, then a
second call saying it has dropped to 100Mbps, if your
cables/connectors are bad.
If your hardware has problems, it might be safest to stop everything
in the callback, make configuration changes, and they start everything
back up. A link negotiation change is not something you expect to
happen often. So making it slow but robust is O.K.
Andrew
next prev parent reply other threads:[~2017-12-06 16:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-06 16:39 Waiting for the PHY to complete auto-negotiation Mason
2017-12-06 16:59 ` Andrew Lunn [this message]
2017-12-06 18:03 ` Mason
2017-12-06 18:26 ` Andrew Lunn
2017-12-06 19:00 ` Mason
2017-12-06 19:07 ` Andrew Lunn
2017-12-06 19:25 ` Mason
2017-12-06 23:00 ` Florian Fainelli
2017-12-07 16:17 ` Mason
2017-12-09 18:49 ` Florian Fainelli
2017-12-11 14:29 ` Mason
2017-12-11 14:36 ` Måns Rullgård
2017-12-11 14:47 ` Mason
2017-12-11 16:32 ` Måns Rullgård
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