CL37 autonegotiation not working on amd-xgbe

CL37 autonegotiation not working on amd-xgbe

[Patrick Oppenlander]

Hi,

A recent change [1] stopped CL37 autonegotiation from working on
amd-xgbe hardware.

The driver thinks autonegotiation is succeeding, but no data is able
to transfer across the link. Here's an mdio/phy debug log showing the
link coming up successfully in the broken state:

amd-xgbe 0000:07:00.2 control-sfp: phy powered off
amd-xgbe 0000:07:00.2 control-sfp: CL73 AN disabled
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN disabled
amd-xgbe 0000:07:00.2 control-sfp: starting PHY
amd-xgbe 0000:07:00.2 control-sfp: 10GbE SFI mode set
amd-xgbe 0000:07:00.2 control-sfp: 1GbE X mode set
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN (BaseX) initialized
amd-xgbe 0000:07:00.2 control-sfp: AN PHY configuration
amd-xgbe 0000:07:00.2 control-sfp: CL73 AN disabled
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN disabled
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN (BaseX) initialized
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN enabled/restarted
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN Complete
amd-xgbe 0000:07:00.2 control-sfp: Auto negotiation successful
amd-xgbe 0000:07:00.2 control-sfp: CL37 AN result: Complete
amd-xgbe 0000:07:00.2 control-sfp: Link is Up - 1Gbps/Full - flow control off

I've tried SFP modules and switches from multiple vendors, and no
combination of hardware successfully autonegotiates after the change.

Unfortunately there appears to be no public documentation available
for amd-xgbe, so it's basically impossible for me to debug any
further. I've included a patch which "fixes" the issue, but given the
lack of documentation I have no idea what it really does.

If there's any more information I can provide to help diagnose the
issue, please let me know.

Patrick

[1] https://patch.msgid.link/20250630192636.3838291-1-Raju.Rangoju@amd.com

-- >8 --

From d17b2e685cc0e389f9c62b6cae735b2ef7d8c49b Mon Sep 17 00:00:00 2001
From: Patrick Oppenlander <patrick.oppenlander@gmail.com>
Date: Thu, 23 Apr 2026 09:37:51 +1000
Subject: [PATCH] amd-xgbe: fix CL37 autonegotiation

Broken after 42fd432fe6d320323215ebdf4de4d0d7e56e6792.

I can't find any documentation for this hardware, so this change really
just reverts the part of the commit which made autonegotation stop
working.
---
 drivers/net/ethernet/amd/xgbe/xgbe-mdio.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
index e4334c12b3e15..7639961db0af4 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
@@ -377,10 +377,6 @@ static void xgbe_an37_set(struct xgbe_prv_data
*pdata, bool enable,
         reg |= MDIO_VEND2_CTRL1_AN_RESTART;

     XMDIO_WRITE(pdata, MDIO_MMD_VEND2, MDIO_CTRL1, reg);
-
-    reg = XMDIO_READ(pdata, MDIO_MMD_VEND2, MDIO_PCS_DIG_CTRL);
-    reg |= XGBE_VEND2_MAC_AUTO_SW;
-    XMDIO_WRITE(pdata, MDIO_MMD_VEND2, MDIO_PCS_DIG_CTRL, reg);
 }

 static void xgbe_an37_restart(struct xgbe_prv_data *pdata)
-- 
2.53.0

Re: CL37 autonegotiation not working on amd-xgbe

[Jakub Kicinski]

On Thu, 23 Apr 2026 10:18:49 +1000 Patrick Oppenlander wrote:
> A recent change [1] stopped CL37 autonegotiation from working on
> amd-xgbe hardware.

Hi Raju! Are you looking into this report?

Re: CL37 autonegotiation not working on amd-xgbe

[Shyam Sundar S K]

+ Prashanth

On 4/28/2026 04:58, Jakub Kicinski wrote:
> On Thu, 23 Apr 2026 10:18:49 +1000 Patrick Oppenlander wrote:
>> A recent change [1] stopped CL37 autonegotiation from working on
>> amd-xgbe hardware.
> 
> Hi Raju! Are you looking into this report?

Dropping Raju as he is no longer with AMD.

Thanks for the bug report. Prashanth will maintain this driver going
forward.

Prashanth, can you address this bug? Also, please update the
MAINTAINERS list by dropping Raju's name.

Thanks,
Shyam

Re: CL37 autonegotiation not working on amd-xgbe

[Thorsten Leemhuis]

On 5/6/26 05:55, Shyam Sundar S K wrote:
> On 4/28/2026 04:58, Jakub Kicinski wrote:
>> On Thu, 23 Apr 2026 10:18:49 +1000 Patrick Oppenlander wrote:
>>> A recent change [1]

FWIW, that was 42fd432fe6d320 ("amd-xgbe: align CL37 AN sequence as per
databook") [v6.16-rc5]

>>> stopped CL37 autonegotiation from working on amd-xgbe hardware.
>>
>> Hi Raju! Are you looking into this report?
> 
> Dropping Raju as he is no longer with AMD.
> 
> Thanks for the bug report. Prashanth will maintain this driver going
> forward.
> 
> Prashanth, can you address this bug? Also, please update the
> MAINTAINERS list by dropping Raju's name.
Any progress? It looks like nothing happened to fix this regression
since above mail, but I'm looking at things from the outside and there
it's easy to miss something, so please tell me if that's the case.

Ciao, Thorsten

RE: CL37 autonegotiation not working on amd-xgbe

[K.R, Prashanth Kumar]

AMD General

-----Original Message-----
From: Thorsten Leemhuis <regressions@leemhuis.info>
Sent: Wednesday, June 3, 2026 3:57 PM
To: S-k, Shyam-sundar <Shyam-sundar.S-k@amd.com>; Jakub Kicinski <kuba@kernel.org>; K.R, Prashanth Kumar <PrashanthKumar.K.R@amd.com>; Banavara, Madhu <Madhu.Banavara@amd.com>
Cc: Patrick Oppenlander <patrick.oppenlander@gmail.com>; netdev@vger.kernel.org; Linux kernel regressions list <regressions@lists.linux.dev>
Subject: Re: CL37 autonegotiation not working on amd-xgbe

Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.


On 5/6/26 05:55, Shyam Sundar S K wrote:
> On 4/28/2026 04:58, Jakub Kicinski wrote:
>> On Thu, 23 Apr 2026 10:18:49 +1000 Patrick Oppenlander wrote:
>>> A recent change [1]

FWIW, that was 42fd432fe6d320 ("amd-xgbe: align CL37 AN sequence as per
databook") [v6.16-rc5]

>>> stopped CL37 autonegotiation from working on amd-xgbe hardware.
>>
>> Hi Raju! Are you looking into this report?
>
> Dropping Raju as he is no longer with AMD.
>
> Thanks for the bug report. Prashanth will maintain this driver going
> forward.
>
> Prashanth, can you address this bug? Also, please update the
> MAINTAINERS list by dropping Raju's name.
Any progress? It looks like nothing happened to fix this regression since above mail, but I'm looking at things from the outside and there it's easy to miss something, so please tell me if that's the case.

Ciao, Thorsten

Thanks for the follow-up.
A fix has been identified and a patch is prepared. We are currently running regression testing to ensure the fix does not introduce any unintended issues. We will share the patch on the mailing list once regression validation is complete.

Thanks for your patience.

Regards,
Prashanth

✅ You can use this draft directly in Outlook and tweak tone if needed (e.g., more technical detail or adding commit reference).