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

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Date:   Tue, 7 Feb 2023 15:41:35 +0100
From:   Clément Léger <clement.leger@...tlin.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Sergey Shtylyov <s.shtylyov@....ru>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Wong Vee Khee <veekhee@...le.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Revanth Kumar Uppala <ruppala@...dia.com>,
        Tan Tee Min <tee.min.tan@...ux.intel.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Herve Codina <herve.codina@...tlin.com>,
        Miquèl Raynal <miquel.raynal@...tlin.com>,
        Milan Stevanovic <milan.stevanovic@...com>,
        Jimmy Lalande <jimmy.lalande@...com>,
        Pascal Eberhard <pascal.eberhard@...com>,
        Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>,
        Jon Hunter <jonathanh@...dia.com>, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next 3/6] net: stmmac: start phylink before setting
 up hardware

Le Mon, 16 Jan 2023 10:53:49 +0000,
"Russell King (Oracle)" <linux@...linux.org.uk> 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