AW: assert in phylink.c with lan7801 and dp83tc811 since kernel 6.18

[Sven Schuchmann <schuchmann@schleissheimer.de>]

Hi,

> > Von: Andrew Lunn <andrew@lunn.ch>
> > Gesendet: Mittwoch, 06. Mai 2026 15:18
> > An: Maxime Chevallier <maxime.chevallier@bootlin.com>
> > Cc: Sven Schuchmann <schuchmann@schleissheimer.de>; netdev@vger.kernel.org <netdev@vger.kernel.org>
> > Betreff: Re: assert in phylink.c with lan7801 and dp83tc811 since kernel 6.18
> 
> On Wed, May 06, 2026 at 03:04:42PM +0200, Maxime Chevallier wrote:
> > On 06/05/2026 14:39, Andrew Lunn wrote:
> > >> So for me it somewhere happens in phylink_validate_mac_and_pcs()
> > > I was expecting to see more debug output, but reading the code, i was
> > > also thinking we need to look at phylink_validate_mac_and_pcs().
> > > You are going in the correct direction putting lots of printk() in the
> > > code. We need to find where it returns EINVAL:
> > [...]
> > > In the end, we are probably going to find that what the MAC says its
> 
> > > capabilities are don't match what the PCS says it can do.
> > > Thinking about that, it says phy mode RGMII. You generally don't use a
> > > PCS with RGMII, so that is suspicious.

> > Another thing to consider is that in this case, we're attaching to a
> > dp83tc811, so a 100BaseT1 PHY. Does the PHY driver correctly populates
> > the supported features ?

> Using RGMII to connect to a 100BaseT is also odd. It does happen, but
> it is a bit of a corner case, and something could be going wrong here.

What I can at least say that it was working with kernel 6.12 on 
the same hardware. But I do not know about the supported features population.

I added some debug code to the end of phylink_validate_mac_and_pcs():

	/* Then validate the link parameters with the MAC */
	if (pl->mac_ops->mac_get_caps)
		capabilities = pl->mac_ops->mac_get_caps(pl->config,
							 state->interface);
	else
		capabilities = pl->config->mac_capabilities;

	phylink_validate_mask_caps(supported, state, capabilities);

	phylink_dbg(pl, "phy: --3.4 supported    0x%x\n", supported);
	phylink_dbg(pl, "phy: --3.4 capabilities 0x%x\n", capabilities);

	int retval = phylink_is_empty_linkmode(supported) ? -EINVAL : 0;
	phylink_dbg(pl, "phy: --3.5-- %d\n", retval);
	return retval;
}

and the output I get is:
[    2.771602] lan78xx 1-1.4:1.0 (unnamed net_device) (uninitialized): phy: --3.4 supported    0x80cf3430
[    2.771607] lan78xx 1-1.4:1.0 (unnamed net_device) (uninitialized): phy: --3.4 capabilities 0xbf
[    2.771611] lan78xx 1-1.4:1.0 (unnamed net_device) (uninitialized): phy: --3.5-- -22
[    2.771616] lan78xx 1-1.4:1.0 (unnamed net_device) (uninitialized): validation of rgmii-id with support 00000000,00000000,00000000,00006280 and advertisement 00000000,00000000,00000000,00006280 failed: -EINVAL

But I do not get what phylink_is_empty_linkmode() is doing...

Regards,

   Sven