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

[Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>]

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@rmk-PC.armlinux.org.uk/
> 
> 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.

	Ayaan