netdev - Re: [PATCH net-next 1/2] net: phylink: explicitly configure in-band autoneg for PHYs that support it

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Message-ID: <4b3f06686cb58dcdda582bfdbd0abb85@walle.cc>
Date:   Sat, 13 Feb 2021 20:57:46 +0100
From:   Michael Walle <michael@...le.cc>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Antoine Tenart <atenart@...nel.org>,
        Quentin Schulz <quentin.schulz@...tlin.com>,
        netdev@...r.kernel.org, Heiner Kallweit <hkallweit1@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next 1/2] net: phylink: explicitly configure in-band
 autoneg for PHYs that support it

Am 2021-02-13 19:56, schrieb Vladimir Oltean:
> On Sat, Feb 13, 2021 at 06:09:13PM +0100, Michael Walle wrote:
>> Am 2021-02-13 17:53, schrieb Michael Walle:
>> > Am 2021-02-13 01:36, schrieb Vladimir Oltean:
>> > But the Atheros PHY seems to have a problem with the SGMII link
>> > if there is no autoneg.
>> > No matter what I do, I can't get any traffic though if its not
>> > gigabit on the copper side. Unfortunately, I don't have access
>> > to an oscilloscope right now to see whats going on on the SGMII
>> > link.
>> 
>> Scrap that. It will work if I set the speed/duplex mode in BMCR
>> correctly. (I tried that before, but I shifted one bit. doh).
>> 
>> So that will work, but when will it be done? There is no
>> callback to configure the PCS side of the PHY if a link up is
>> detected.
> 
> That's interesting/odd, on VSC8514 there is no need to force the speed
> of the system side to what was negotiated on media side. I took a quick
> look through the AR8033 datasheet and there isn't any mentioning the
> ability to program the SGMII link according to internal state as 
> opposed
> to register settings, but it's equally possible that I'm simply not
> seeing it.

I couldn't find anything in the AR8031 datasheet either.

> On the other hand, I never meant for the inband autoneg setting to only
> be configurable both ways.

Then why is there a "bool enabled"?

> I expect some PHYs are not able to operate
> using noinband mode, and for those I guess you should simply return
> -EINVAL, allowing the system designer to know that the configuration
> will not work and why.

You mean like this:

static int at803x_config_inband_aneg(struct phy_device *phydev, bool 
enabled)
{
	if (!enabled)
		return -EINVAL;
	/* enable SGMII autoneg */
	return phy_write_paged(...);
}

But then why bother with config_inband_aneg() at all and just enable
it unconditionally in config_init(). [and maybe keep the return 
-EINVAL].
Which then begs the question, does it makes sense on (Q)SGMII links at
all?

> I think you could hook into .config_aneg_done, for the autoneg=true
> case, and into .config_aneg for autoneg=false (I'm talking about 
> autoneg
> on media side here), but honestly I think the PHY is pretty broken for
> requiring external coordination between the clause 28 and the clause 37
> PCS. So unless there is a real need to configure noinband mode, I would
> probably not bother.

Probably not.

-michael