netdev - RE: [PATCH v1 1/1] net: phy: micrel: Add workaround for incomplete autonegotiation

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Date: Fri, 19 Jan 2024 22:57:10 +0000
From: Asmaa Mnebhi <asmaa@...dia.com>
To: Andrew Lunn <andrew@...n.ch>
CC: "Russell King (Oracle)" <linux@...linux.org.uk>, "davem@...emloft.net"
	<davem@...emloft.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Thompson <davthompson@...dia.com>
Subject: RE: [PATCH v1 1/1] net: phy: micrel: Add workaround for incomplete
 autonegotiation

> 
> > The above prints proved that the micrel PHY started autonegotiation
> > but the result is that it failed to complete it. I also noticed that
> > the KSZ9031 PHY takes ~5 full seconds to complete aneg which is much
> > longer than other PHYs like VSC8221 (which we use with BlueField-3
> > systems).
> 
> What is the link partner? From the datasheet
> 
> MMD Address 1h, Register 5Ah – 1000BASE-T Link-Up Time Control
> 
> When the link partner is another KSZ9031 device, the 1000BASE-T link-up time
> can be long. These three bits provide an optional setting to reduce the
> 1000BASE-T link-up time.
> 100 = Default power-up setting
> 011 = Optional setting to reduce link-up time when the link partner is a KSZ9031
> device.
> 
> Might be worth setting it and see what happens.
> 
> Have you tried playing with the prefer master/prefer slave options? If you have
> identical PHYs on each end, it could be they are generating the same 'random'
> number used to determine who should be master and who should be slave. If
> they both pick the same number, they are supposed to pick a different random
> number and try again. There have been some PHYs which are broken in this
> respect. prefer master/prefer slave should influence the random number,
> biasing it higher/lower.
> 
> auto-neg should typically take a little over 1 second. 5 seconds is way too long,
> something is not correct. You might want to sniff the fast link pulses, try to
> decode the values and see what is going on.
> 
> I would not be surprised if you find out this 5 second complete time is somehow
> related to it not completing at all.
>

The link partner is a switch (KSZ9893R) so I am not sure setting the 5Ah register to 011 would help.