netdev - Re: [PATCH net-next 8/8] net: phy: marvell10g: select host interface configuration

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Date:   Thu, 18 Nov 2021 14:56:58 +0100
From:   Marek Behún <kabel@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 8/8] net: phy: marvell10g: select host
 interface configuration

On Thu, 18 Nov 2021 14:03:34 +0200
Vladimir Oltean <olteanv@...il.com> wrote:

> Hello,
> 
> > +static int mv3310_select_mactype(unsigned long *interfaces)
> > +{
> > +	if (test_bit(PHY_INTERFACE_MODE_USXGMII, interfaces))
> > +		return MV_V2_33X0_PORT_CTRL_MACTYPE_USXGMII;
> > +	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces) &&
> > +		 test_bit(PHY_INTERFACE_MODE_10GBASER, interfaces))
> > +		return MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER;
> > +	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces) &&
> > +		 test_bit(PHY_INTERFACE_MODE_RXAUI, interfaces))
> > +		return MV_V2_33X0_PORT_CTRL_MACTYPE_RXAUI;
> > +	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces) &&
> > +		 test_bit(PHY_INTERFACE_MODE_XAUI, interfaces))
> > +		return MV_V2_3310_PORT_CTRL_MACTYPE_XAUI;
> > +	else if (test_bit(PHY_INTERFACE_MODE_10GBASER, interfaces))
> > +		return MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER_RATE_MATCH;
> > +	else if (test_bit(PHY_INTERFACE_MODE_RXAUI, interfaces))
> > +		return MV_V2_33X0_PORT_CTRL_MACTYPE_RXAUI_RATE_MATCH;
> > +	else if (test_bit(PHY_INTERFACE_MODE_XAUI, interfaces))
> > +		return MV_V2_3310_PORT_CTRL_MACTYPE_XAUI_RATE_MATCH;
> > +	else if (test_bit(PHY_INTERFACE_MODE_SGMII, interfaces))
> > +		return MV_V2_33X0_PORT_CTRL_MACTYPE_10GBASER;
> > +	else
> > +		return -1;
> > +}
> > +  
> 
> I would like to understand this heuristic better. Both its purpose and
> its implementation.
> 
> It says:
> (a) If the intersection between interface modes supported by the MAC and
>     the PHY contains USXGMII, then use USXGMII as a MACTYPE
> (b) Otherwise, if the intersection contains both 10GBaseR and SGMII, then
>     use 10GBaseR as MACTYPE
> (...)
> (c) Otherwise, if the intersection contains just 10GBaseR (no SGMII), then
>     use 10GBaseR with rate matching as MACTYPE
> (...)
> (d) Otherwise, if the intersection contains just SGMII (no 10GBaseR), then
>     use 10GBaseR as MACTYPE (no rate matching).
> 
> First of all, what is MACTYPE exactly? And what is the purpose of
> changing it? What would happen if this configuration remained fixed, as
> it were?
> 
> I see there is no MACTYPE definition for SGMII. Why is that? How does
> the PHY choose to use SGMII?
> 
> Why is item (d) correct - use 10GBaseR as MACTYPE if the intersection
> only supports SGMII?
> 
> A breakdown per link speed might be helpful in understanding the
> configurations being performed here.

Russell already explained this. I will put a better explanation into
the commit message in v2.

> >  static int mv2110_init_interface(struct phy_device *phydev, int mactype)
> >  {
> >  	struct mv3310_priv *priv = dev_get_drvdata(&phydev->mdio.dev);
> > @@ -674,10 +764,16 @@ static int mv3310_config_init(struct phy_device *phydev)
> >  {
> >  	struct mv3310_priv *priv = dev_get_drvdata(&phydev->mdio.dev);
> >  	const struct mv3310_chip *chip = to_mv3310_chip(phydev);
> > +	DECLARE_PHY_INTERFACE_MASK(interfaces);
> >  	int err, mactype;
> >  
> > -	/* Check that the PHY interface type is compatible */
> > -	if (!test_bit(phydev->interface, priv->supported_interfaces))
> > +	/* In case host didn't provide supported interfaces */
> > +	__set_bit(phydev->interface, phydev->host_interfaces);  
> 
> Shouldn't phylib populate phydev->host_interfaces with
> phydev->interface, rather than requiring PHY drivers to do it?

I will look into this.

Marek