linux-kernel - Re: [PATCH] net: phy: fix auto-negotiation in case of 'down-shift'

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Date:   Tue, 24 Nov 2020 15:37:50 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Antonio Borneo <antonio.borneo@...com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Yonglong Liu <liuyonglong@...wei.com>, stable@...r.kernel.org,
        linuxarm@...wei.com, Salil Mehta <salil.mehta@...wei.com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: fix auto-negotiation in case of 'down-shift'

On Tue, Nov 24, 2020 at 04:17:42PM +0100, Antonio Borneo wrote:
> On Tue, 2020-11-24 at 14:56 +0000, Russell King - ARM Linux admin wrote:
> > Userspace doesn't expect the advertising mask to change beneath it.
> > Since updates from userspace are done using a read-modify-write of
> > the ksettings, this can have the undesired effect of removing 1G
> > from the configured advertising mask.
> > 
> > We've had other PHYs have this behaviour; the correct solution is for
> > the PHY driver to implement reading the resolution from the PHY rather
> > than relying on the generic implementation if it can down-shift
> 
> If it's already upstream, could you please point to one of the phy driver
> that already implements this properly?

Reading the resolved information is PHY specific as it isn't
standardised.

Marvell PHYs have read the resolved information for a very long time.
I added support for it to at803x.c:

06d5f3441b2e net: phy: at803x: use operating parameters from PHY-specific status

after it broke for exactly the reason you're reporting for your PHY.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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