netdev - Re: LAN8720: RX errors / packet loss when using smsc PHY driver on i.MX6Q

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Message-ID: <CAOMZO5BEcoQSLJpGUtsfiNXPUMVP3kbs1n9KXZxaWBzifZHoZw@mail.gmail.com>
Date: Fri, 14 Nov 2025 18:15:17 -0300
From: Fabio Estevam <festevam@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>, Russell King - ARM Linux <linux@...linux.org.uk>, 
	edumazet <edumazet@...gle.com>, netdev <netdev@...r.kernel.org>
Subject: Re: LAN8720: RX errors / packet loss when using smsc PHY driver on i.MX6Q

Hi Andrew,

On Thu, Nov 13, 2025 at 7:35 PM Andrew Lunn <andrew@...n.ch> wrote:

> Maybe dump all 32 registers when genphy and smsc driver are being used
> and compare them?

The dump of all the 32 registers are identical in both cases:

./mii-diag -vvv
mii-diag.c:v2.11 3/21/2005 Donald Becker (becker@...ld.com)
 http://www.scyld.com/diag/index.html
Using the default interface 'eth0'.
  Using the new SIOCGMIIPHY value on PHY 0 (BMCR 0x3100).
 The autonegotiated capability is 01e0.
The autonegotiated media type is 100baseTx-FD.
 Basic mode control register 0x3100: Auto-negotiation enabled.
 You have link beat, and everything is working OK.
   This transceiver is capable of  100baseTx-FD 100baseTx 10baseT-FD 10baseT.
   Able to perform Auto-negotiation, negotiation complete.
 Your link partner advertised cde1: Flow-control 100baseTx-FD
100baseTx 10baseT-FD 10baseT, w/ 802.3X flow control.
   End of basic transceiver information.

libmii.c:v2.11 2/28/2005  Donald Becker (becker@...ld.com)
 http://www.scyld.com/diag/index.html
 MII PHY #0 transceiver registers:
   3100 782d 0007 c0f1 05e1 cde1 0009 ffff
   ffff ffff ffff ffff ffff ffff ffff 0000
   0040 0002 60e0 ffff 0000 0000 0000 0000
   ffff ffff 0000 000a 0000 00c8 0000 1058.
 Basic mode control register 0x3100: Auto-negotiation enabled.
 Basic mode status register 0x782d ... 782d.
   Link status: established.
   Capable of  100baseTx-FD 100baseTx 10baseT-FD 10baseT.
   Able to perform Auto-negotiation, negotiation complete.
 Vendor ID is 00:01:f0:--:--:--, model 15 rev. 1.
   No specific information is known about this transceiver type.
 I'm advertising 05e1: Flow-control 100baseTx-FD 100baseTx 10baseT-FD 10baseT
   Advertising no additional info pages.
   IEEE 802.3 CSMA/CD protocol.
 Link partner capability is cde1: Flow-control 100baseTx-FD 100baseTx
10baseT-FD 10baseT.
   Negotiation  completed.

After pinging with the Generic PHY driver:

# ethtool -S eth0 | grep error
     tx_crc_errors: 0
     rx_crc_errors: 0
     rx_xdp_tx_errors: 0
     tx_xdp_xmit_errors: 0

After pinging with the SMSC PHY driver:

# ethtool -S eth0 | grep err
     tx_crc_errors: 0
     IEEE_tx_macerr: 0
     IEEE_tx_cserr: 0
     rx_crc_errors: 19
     IEEE_rx_macerr: 0
     rx_xdp_tx_errors: 0
     tx_xdp_xmit_errors: 0

Any ideas?

Thanks