Subject: Re: [PATCH net-next 3/6] net: stmmac: start phylink before setting up hardware

From: Clément Léger <[email-masked]>
Date: Tue, 7 Feb 2023 15:41:35 +0100

Le Mon, 16 Jan 2023 10:53:49 +0000,
"Russell King (Oracle)" <[email-masked]> a écrit :

> On Mon, Jan 16, 2023 at 11:39:23AM +0100, Clément Léger wrote:
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index f2247b8cf0a3..88c941003855 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -3818,6 +3818,12 @@ static int __stmmac_open(struct net_device *dev,
> >  		}
> >  	}
> >  
> > +	/* We need to setup the phy & PCS before accessing the stmmac registers
> > +	 * because in some cases (RZ/N1), if the stmmac IP is not clocked by the
> > +	 * PCS, hardware init will fail because it lacks a RGMII RX clock.
> > +	 */
> > +	phylink_start(priv->phylink);  
> 
> So what happens if you end up with the mac_link_up method being called
> at this point in the driver, before the hardware has been setup ?
> 
> If you use a fixed-link, that's a real possibility.

I actually have this setup. On the board, one GMAC is connected to a
DSA switch using a fixed-link and the other using the PCS such as added
by this series.

From what I see, indeed, the mac_link_up() function is called before
stmmac_hw_setup(). This does not seems to have any effect on my setup
(except making it working of course) but I agree this is clearly not
ideal.

What I could do is adding a function in the miic pcs driver that could
be called from my rzn1 stmmac probe function to actually configure the
PCS at probe time based on the detected "phy-mode". Does that seems
better to you ?

Thanks,

-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com