Re: [PATCH net] net: stmmac: Skip PHY attach if custom PCS is in use

[Maxime Chevallier]

Hi,

On 7/22/26 15:47, Mohd Ayaan Anwar wrote:
> On Wed, Jul 22, 2026 at 03:40:08PM +0200, Maxime Chevallier wrote:
>> Hi,
>>
>> +Mohd
>>
>> On 7/22/26 15:19, Zxyan Zhu wrote:
>>> When a platform provides a custom PCS via the pcs_init callback
>>> (e.g., for USXGMII with in-band autoneg), the MAC's phylink_pcs
>>> is already configured. In this case, phylink validates against
>>> the PCS's supported interfaces and manages link state through
>>> the PCS, so no traditional PHY device is needed.
>>>
>>> Without this, stmmac_init_phy() falls through to the
>>> no-phy-node path and errors out with "no phy found" when
>>> the DT has no phy-handle for such interfaces.
>>>
>>> Skip the PHY attach when priv->hw->phylink_pcs is already set
>>> and no phy-handle is specified in the device tree, allowing
>>> platform PCS implementations to handle the link autonomously.
>>
>> Hmpf this bug again...
>>
>> There have been multiple attempts at solving this, cf this thread :
>>
>> https://lore.kernel.org/netdev/E1w66jW-0000000E3qS-23fW@xxxxxxxxxxxxxxxxxxxxxx/
>>
>> Now, there wasn't any conclusion on that, but I _think_ the proper
>> solution is to re-apply Russell's original patch (the one in the link above)
>> and to add this current patch on top of it.
>>
>> Russell states that this may (will ?) break qcom-ethqos, but OTOH
>> we're in need for a solution here, and with the pace of PCS-related
>> work that impacts stmmac, there's going to be a point where we may
>> need to think about compatibility.
>>
>> TBF I don't understand the qcom-ethqos issue, maybe Mohd can help
>> with testing here ?
>>
> 
> Sure, I can help test out qcom-ethqos and see if and where it breaks.
> 
> We could not arrive at a conclusion the last time because I ran out of
> options to try and find a proper solution. So if it still breaks, I will
> spend some time and brainstorm qcom-ethqos's interaction with the
> integrated PCS, again.

Thanks :) Good to know you're here to test !

Zxyan Zhu, I think you can send a V2 Series with this current patch, as well as
this patch from Russell :

https://lore.kernel.org/netdev/E1w66jW-0000000E3qS-23fW@xxxxxxxxxxxxxxxxxxxxxx/

The combination of the two work on dwmac-socfpga, and it would be great to test
that on other stmmac variants

Maxime