Re: [PATCH net-next v2 00/14] net: stmmac: SerDes, PCS, BASE-X, and inband goodies

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

On Tue, Jan 27, 2026 at 03:42:57PM +0000, Russell King (Oracle) wrote:
> On Tue, Jan 27, 2026 at 08:27:50PM +0530, Mohd Ayaan Anwar wrote:
> > During pcs_init, BIT(8) of GMAC_AN_STATUS is 0:
> > [    7.985913] [DBG] GMAC_AN_STATUS = 8
> 
> Hmm. This means that your hardware doesn't support TBI or RTBI modes
> (which is what the dwmac core uses for BASE-X) and what it's actually
> offering is an up-clocked Cisco SGMII implementation.
> 
> With AN disabled, this is compatible with 2500BASE-X implementations
> that do not require AN.

Yes, this hardware implements what some vendors call OCSGMII (i.e.
2500BASE-X without in-band signalling).

> > I also tried enabling comma detect during dwmac_integrated_pcs_config,
> > but I am still seeing the Tx timeouts. I remember that when I had
> > tested the patches in October (without the SerDes driver changes),
> > the link state used to flap, but the data path became functional
> > after the link stabilized.
> 
> I wonder whether the SerDes needs to be calibrated after the link has
> come up and the clocks configured. phy_calibdate() will re-invoke the
> programming of the SerDes, so you could try adding that at the bottom
> of ethqos_configure_sgmii():
> 
> 	return phy_calibrate(priv->plat->serdes);
> 
> which will do the calibration after the clocks have been set, and see
> whether that stabilises the link.

Somehow booting up with a 2.5G link is more unstable after adding this.
Behaviour at 1G is pretty similar. I kept comma detection disabled
during these tests.

I was thinking about the "good" sequence (i.e., the current net-next
tree):
	-> phylink_up
	  -> mac_link_up
	    -> fix_mac_speed
	      -> SerDes configured via phy_set_speed
	      -> stmmac_pcs_ctrl_ane(priv, enable/disable, 0)

Please let me know if you want me to try any other experiments.
Maybe I need to do some more testing after playing around with the
sequence followed by this series?

	Ayaan