linux-kernel - Re: [PATCH 2/2] net: dsa: microchip: Provide Module 4 KSZ9477 errata (DS80000754C)

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Date:   Tue, 29 Aug 2023 19:12:05 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Vladimir Oltean <olteanv@...il.com>, Tristram.Ha@...rochip.com,
        Oleksij Rempel <linux@...pel-privat.de>,
        Arun Ramadoss <arun.ramadoss@...rochip.com>,
        f.fainelli@...il.com, andrew@...n.ch, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, Woojung.Huh@...rochip.com,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH 2/2] net: dsa: microchip: Provide Module 4 KSZ9477 errata
 (DS80000754C)

On Tue, Aug 29, 2023 at 05:29:13PM +0200, Lukasz Majewski wrote:
> Hi Oleksij,
> > On other hand, since this functionality is not listed as supported by
> > the KSZ9477 datasheet (No word about IEEE 802.3az Energy Efficient
> > Ethernet (EEE)) compared to KSZ8565R datasheet (where EEE support is
> > listed) and it is confirmed to work not stable enough, then it should
> > be disabled properly.
> 
> I've described this problem in more details here:
> https://lore.kernel.org/lkml/20230829132429.529283be@wsk/
> 
> -------->8---------
> The issue is that ksz9477_config_init() (drivers/net/phy/micrel.c) is
> executed AFTER generic phy_probe():
> https://elixir.bootlin.com/linux/latest/source/drivers/net/phy/phy_device.c#L3256
> in which the EEE advertisement registers are read.
> 
> Hence, those registers needs to be cleared earlier - as I do in
> ksz9477_setup() in drivers/net/dsa/microchip/ksz9477.
> 
> Here the precedence matters ...
> ----------8<-------------
> 
> > The phydev->supported_eee should be cleared.
> > See ksz9477_get_features().
> > 
> 
> Removing the linkmod_and() from ksz9477_get_features():
> https://elixir.bootlin.com/linux/latest/source/drivers/net/phy/micrel.c#L1408
> 
> doesn't help.

Yes, removing linkmod_and() will not should not help. I said, "The
phydev->supported_eee should be cleared."

For example like this:
--- a/drivers/net/phy/micrel.c
+++ b/drivers/net/phy/micrel.c
@@ -1400,6 +1400,7 @@ static int ksz9131_config_aneg(struct phy_device *phydev)
 
 static int ksz9477_get_features(struct phy_device *phydev)
 {
+       __ETHTOOL_DECLARE_LINK_MODE_MASK(zero) = { 0, };
        int ret;
 
        ret = genphy_read_abilities(phydev);
@@ -1413,7 +1414,7 @@ static int ksz9477_get_features(struct phy_device *phydev)
         * KSZ8563R should have 100BaseTX/Full only.
         */
        linkmode_and(phydev->supported_eee, phydev->supported,
-                    PHY_EEE_CAP1_FEATURES);
+                    zero);
 
        return 0;
 }

You will need to clear it only on KSZ9477 variants with this bug.
This change is tested and it works on my KSZ9477-EVB.

Regards,
Oleksij
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