linux-kernel - Re: [PATCH net-next 3/4] net: phy: Add helper to derive the number of ports from a phy mode

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Date:   Fri, 29 Jul 2022 15:00:05 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     davem@...emloft.net, Rob Herring <robh+dt@...nel.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, thomas.petazzoni@...tlin.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, Horatiu.Vultur@...rochip.com,
        Allan.Nielsen@...rochip.com, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next 3/4] net: phy: Add helper to derive the number
 of ports from a phy mode

On Fri, Jul 29, 2022 at 09:32:52AM +0200, Maxime Chevallier wrote:
> On Thu, 28 Jul 2022 23:32:36 +0200
> Andrew Lunn <andrew@...n.ch> wrote:
> 
> > > +int phy_interface_num_ports(phy_interface_t interface)
> > > +{
> > > +	switch (interface) {
> > > +	case PHY_INTERFACE_MODE_NA:
> > > +	case PHY_INTERFACE_MODE_INTERNAL:
> > > +		return 0;  
> > 
> > I've not yet looked at how this is used. Returning 0 could have
> > interesting effects i guess? INTERNAL clearly does have some sort of
> > path between the MAC and the PHY, so i think 1 would be a better
> > value. NA is less clear, it generally means Don't touch. But again,
> > there still needs to be a path between the MAC and PHY, otherwise
> > there would not be any to touch.
> > 
> > Why did you pick 0?
> > 
> > > +
> > > +	case PHY_INTERFACE_MODE_MII:
> > > +	case PHY_INTERFACE_MODE_GMII:
> > > +	case PHY_INTERFACE_MODE_TBI:
> > > +	case PHY_INTERFACE_MODE_REVMII:
> > > +	case PHY_INTERFACE_MODE_RMII:
> > > +	case PHY_INTERFACE_MODE_REVRMII:
> > > +	case PHY_INTERFACE_MODE_RGMII:
> > > +	case PHY_INTERFACE_MODE_RGMII_ID:
> > > +	case PHY_INTERFACE_MODE_RGMII_RXID:
> > > +	case PHY_INTERFACE_MODE_RGMII_TXID:
> > > +	case PHY_INTERFACE_MODE_RTBI:
> > > +	case PHY_INTERFACE_MODE_XGMII:
> > > +	case PHY_INTERFACE_MODE_XLGMII:
> > > +	case PHY_INTERFACE_MODE_MOCA:
> > > +	case PHY_INTERFACE_MODE_TRGMII:
> > > +	case PHY_INTERFACE_MODE_USXGMII:
> > > +	case PHY_INTERFACE_MODE_SGMII:
> > > +	case PHY_INTERFACE_MODE_SMII:
> > > +	case PHY_INTERFACE_MODE_1000BASEX:
> > > +	case PHY_INTERFACE_MODE_2500BASEX:
> > > +	case PHY_INTERFACE_MODE_5GBASER:
> > > +	case PHY_INTERFACE_MODE_10GBASER:
> > > +	case PHY_INTERFACE_MODE_25GBASER:
> > > +	case PHY_INTERFACE_MODE_10GKR:
> > > +	case PHY_INTERFACE_MODE_100BASEX:
> > > +	case PHY_INTERFACE_MODE_RXAUI:
> > > +	case PHY_INTERFACE_MODE_XAUI:
> > > +		return 1;
> > > +	case PHY_INTERFACE_MODE_QSGMII:
> > > +	case PHY_INTERFACE_MODE_QUSGMII:
> > > +		return 4;
> > > +
> > > +	default:
> > > +		return 0;
> > > +	}
> > > +}  
> > 
> > Have you tried without a default: ? I _think_ gcc will then warn about
> > missing enum values, which will help future developers when they add
> > further values to the enum.
> 
> Without the default clause, I get an error about the missing
> PHY_INTERFACE_MODE_MAX case, which I don't think belongs here...

  case PHY_INTERFACE_MODE_MAX:
	WARN_ONCE()
	return 0;
	break;

Being passed PHY_INTERFACE_MODE_MAX is a bug in itself, so warning
seems sensible.

      Andrew