Re: [PATCH net 2/2] net: stmmac: qcom-ethqos: advertise supported SerDes interfaces

[Coia Prant]

Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx> 于2026年9月17日周四 13:36写道：
>
> Hi Thomas,
>
> +Coia
>
> On 9/17/26 06:29, Thomas Karpiniec wrote:
>
> >> Can you test settung the STMMAC_FLAG_SERDES_SUPPORTS_2500M flag in
> >> dwmac-qcom-ethqos ?
> >
> > I can confirm that dma_cap.pcs = Y.
>
> Thanks for looking up :) This is a good start
>
> >
> > I tested setting STMMAC_FLAG_SERDES_SUPPORTS_2500M on hardware and unfortunately the flag alone doesn't solve the problem.
>
> Yeah, but it's still the right first move. Russell planned to do that as well :
>
> https://lore.kernel.org/netdev/E1vvDJi-0000000ArhH-3ipf@xxxxxxxxxxxxxxxxxxxxxx/#t
>
> >
> > I think there are a couple of things missing. stmmac_phylink_setup doesn't use the integrated PCS bitmap to populate config->supported_interfaces, so SGMII is still not advertised to phylink as a usable host interface. Also stmmac_integrated_pcs_init is adding 1000BASE-X unconditionally, which wouldn't be appropriate here.
>
> Ok so, the missing bit seems to be that priv->integrated_pcs isn't taken
> into account in stmmac_phylink_setup(). This needs to be added then :)
>
> Looks like there's also the inband support that needs addressing, that was
> part of his RFC here :
>
> https://lore.kernel.org/netdev/E1vvDJi-0000000ArhH-3ipf@xxxxxxxxxxxxxxxxxxxxxx/#t
>
> > I did a proof-of-concept fixing those things and the end result looks a little messy: config->supported_interfaces could come from either get_interfaces _or_ the integrated PCS with unclear (to me) responsibility.
>
> There's only dwmac-intel, dwmac-spacemit and dwmac-rk that use the
> .get_interfaces() API. Let me add Coia in CC, as they're working
> on better PCS support specifically for Rockchip :
>
> https://lore.kernel.org/netdev/20260915123802.1561724-1-coiaprant@xxxxxxxxx/
>
> For spacemit, looks like it's not really a problem as there's no PCS
> involved. For intel though, heh... Intel platforms with dwmac AND PCS
> are hard to come by, but I think at that point let's roll with the
> bitwise or'int of get_interfaces + pcs interfaces.
>
> > This POC did show that STMMAC_FLAG_SERDES_SUPPORTS_2500M enabled phylink to configure the integrated PCS for 2500BASE-X and a 2.5 Gbps link came up with no apparent issues.
>
> Maybe the blind spot is inband aneg. Mohd, you were quite involved in
> this, do you remember where we stand on that front ?
>
> Thanks,
>
> Maxime

Thanks for adding me.

For the Rockchip side, rk_get_interfaces() no longer needs to advertise
SGMII: stmmac_phylink_setup() already OR's the PCS's supported_interfaces
into config->supported_interfaces, and the XPCS driver provides SGMII
there. I'll drop the SGMII line from rk_get_interfaces() so RGMII ports
don't advertise SGMII unnecessarily.

On the qcom issue: the missing bit seems to be that
stmmac_phylink_setup() only looks at priv->hw->xpcs and
priv->hw->phylink_pcs, not priv->integrated_pcs. Extending the existing
OR to cover the integrated PCS would let qcom-ethqos work without a
new get_interfaces() callback.

Best,
Coia