linux-kernel - Re: [PATCH net-next 04/12] net: pcs: add Renesas MII converter driver

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Date:   Thu, 14 Apr 2022 17:14:08 +0200
From:   Clément Léger <clement.leger@...tlin.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Heiner Kallweit <hkallweit1@...il.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>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 04/12] net: pcs: add Renesas MII converter
 driver

Le Thu, 14 Apr 2022 13:49:08 +0100,
"Russell King (Oracle)" <linux@...linux.org.uk> a écrit :

> On Thu, Apr 14, 2022 at 02:22:42PM +0200, Clément Léger wrote:
> > Add PCS driver for the MII converter that is present on Renesas RZ/N1
> > SoC. This MII converter is reponsible of converting MII to RMII/RGMII
> > or act as a MII passtrough. Exposing it as a PCS allows to reuse it
> > in both the switch driver and the stmmac driver. Currently, this driver
> > only allows the PCS to be used by the dual Cortex-A7 subsystem since
> > the register locking system is not used.  
> 
> Hi,
> 
> > +#define MIIC_CONVCTRL_CONV_MODE		GENMASK(4, 0)
> > +#define CONV_MODE_MII			0
> > +#define CONV_MODE_RMII			BIT(2)
> > +#define CONV_MODE_RGMII			BIT(3)
> > +#define CONV_MODE_10MBPS		0
> > +#define CONV_MODE_100MBPS		BIT(0)
> > +#define CONV_MODE_1000MBPS		BIT(1)  
> 
> Is this really a single 4-bit wide field? It looks like two 2-bit fields
> to me.

You are right, the datasheet presents that as a single bitfield but
that can be split.

> 
> > +#define phylink_pcs_to_miic_port(pcs) container_of((pcs), struct miic_port, pcs)  
> 
> I prefer a helper function to a preprocessor macro for that, but I'm not
> going to insist on that point.

Acked.

> 
> > +static void miic_link_up(struct phylink_pcs *pcs, unsigned int mode,
> > +			 phy_interface_t interface, int speed, int duplex)
> > +{
> > +	struct miic_port *miic_port = phylink_pcs_to_miic_port(pcs);
> > +	struct miic *miic = miic_port->miic;
> > +	int port = miic_port->port;
> > +	u32 val = 0;
> > +
> > +	if (duplex == DUPLEX_FULL)
> > +		val |= MIIC_CONVCTRL_FULLD;
> > +
> > +	switch (interface) {
> > +	case PHY_INTERFACE_MODE_RMII:
> > +		val |= CONV_MODE_RMII;
> > +		break;
> > +	case PHY_INTERFACE_MODE_RGMII:
> > +		val |= CONV_MODE_RGMII;
> > +		break;
> > +	case PHY_INTERFACE_MODE_MII:
> > +		val |= CONV_MODE_MII;
> > +		break;
> > +	default:
> > +		dev_err(miic->dev, "Unsupported interface %s\n",
> > +			phy_modes(interface));
> > +		return;
> > +	}  
> 
> Why are you re-decoding the interface mode? The interface mode won't
> change as a result of a call to link-up. Changing the interface mode
> is a major configuration event that will always see a call to your
> miic_config() function first.

Indeed, seems stupid, I will simply keep the mode bits once split from
speed.

[...]

> > +};
> > +
> > +struct phylink_pcs *miic_create(struct device_node *np)
> > +{
> > +	struct platform_device *pdev;
> > +	struct miic_port *miic_port;
> > +	struct device_node *pcs_np;
> > +	u32 port;
> > +
> > +	if (of_property_read_u32(np, "reg", &port))
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	if (port >= MIIC_MAX_NR_PORTS)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	/* The PCS pdev is attached to the parent node */
> > +	pcs_np = of_get_parent(np);
> > +	if (!pcs_np)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	pdev = of_find_device_by_node(pcs_np);
> > +	if (!pdev || !platform_get_drvdata(pdev))
> > +		return ERR_PTR(-EPROBE_DEFER);  
> 
> It would be a good idea to have a comment in the probe function to say
> that this relies on platform_set_drvdata() being the very last thing
> after a point where initialisation is complete and we won't fail.

Yep, sounds like a good idea.

> 
> Thanks!
> 

Thanks for the review,

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