netdev - Re: [BUG] net: phy: genphy_loopback: add link speed configuration

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Date:   Tue, 14 Dec 2021 10:39:25 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     "Ismail, Mohammad Athari" <mohammad.athari.ismail@...el.com>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Voon, Weifeng" <weifeng.voon@...el.com>,
        "Wong, Vee Khee" <vee.khee.wong@...el.com>
Subject: Re: [BUG] net: phy: genphy_loopback: add link speed configuration

On Tue, Dec 14, 2021 at 07:00:37AM +0000, Ismail, Mohammad Athari wrote:
> Hi Oleksij,
> 
> "net: phy: genphy_loopback: add link speed configuration" patch causes Marvell 88E1510 PHY not able to perform PHY loopback using ethtool command (ethtool -t eth0 offline). Below is the error message: 
> 
> "Marvell 88E1510 stmmac-3:01: genphy_loopback failed: -110" 

-110 is ETIMEDOUT. So that points to the phy_read_poll_timeout().

Ah, that points to the fact the Marvell PHYs are odd. You need to
perform a software reset after changing some registers to actually
execute the change.

As a quick test, please could you try:

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 74d8e1dc125f..b45f3ffc7c7f 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -2625,6 +2625,10 @@ int genphy_loopback(struct phy_device *phydev, bool enable)
 
                phy_modify(phydev, MII_BMCR, ~0, ctl);
 
+               ret = genphy_soft_reset(phydev);
+               if (ret < 0)
+                       return ret;
+
                ret = phy_read_poll_timeout(phydev, MII_BMSR, val,
                                            val & BMSR_LSTATUS,
                                    5000, 500000, true);

If this fixes it for you, the actual fix will be more complex, Marvell
cannot use genphy_loopback, it will need its own implementation.

       Andrew