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

From: "Clément Léger" <clement.leger@bootlin.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: "Sergey Shtylyov" <s.shtylyov@omp.ru>,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Magnus Damm" <magnus.damm@gmail.com>,
	"Giuseppe Cavallaro" <peppe.cavallaro@st.com>,
	"Alexandre Torgue" <alexandre.torgue@foss.st.com>,
	"Jose Abreu" <joabreu@synopsys.com>,
	"Maxime Coquelin" <mcoquelin.stm32@gmail.com>,
	"Wong Vee Khee" <veekhee@apple.com>,
	"Kurt Kanzenbach" <kurt@linutronix.de>,
	"Revanth Kumar Uppala" <ruppala@nvidia.com>,
	"Tan Tee Min" <tee.min.tan@linux.intel.com>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Herve Codina" <herve.codina@bootlin.com>,
	"Miquèl Raynal" <miquel.raynal@bootlin.com>,
	"Milan Stevanovic" <milan.stevanovic@se.com>,
	"Jimmy Lalande" <jimmy.lalande@se.com>,
	"Pascal Eberhard" <pascal.eberhard@se.com>,
	"Mohammad Athari Bin Ismail" <mohammad.athari.ismail@intel.com>,
	"Jon Hunter" <jonathanh@nvidia.com>,
	netdev@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH net-next 3/6] net: stmmac: start phylink before setting up hardware
Date: Tue, 7 Feb 2023 15:41:35 +0100	[thread overview]
Message-ID: <20230207154135.6f0e59f8@fixe.home> (raw)
In-Reply-To: <Y8UsvREsKOR2ejzT@shell.armlinux.org.uk>

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