netdev - Re: [PATCH v1 1/3] net: phy: Allow mdio buses to auto-probe c45 devices

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Date:   Thu, 18 Jun 2020 19:30:30 +0530
From:   Calvin Johnson <calvin.johnson@....nxp.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Jeremy Linton <jeremy.linton@....com>, Jon <jon@...id-run.com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Andrew Lunn <andrew@...n.ch>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        netdev@...r.kernel.org, linux.cj@...il.com
Subject: Re: [PATCH v1 1/3] net: phy: Allow mdio buses to auto-probe c45
 devices

On Wed, Jun 17, 2020 at 06:44:51PM +0100, Russell King - ARM Linux admin wrote:
> On Wed, Jun 17, 2020 at 10:45:33PM +0530, Calvin Johnson wrote:
> > From: Jeremy Linton <jeremy.linton@....com>
> > 
> > The mdiobus_scan logic is currently hardcoded to only
> > work with c22 devices. This works fairly well in most
> > cases, but its possible a c45 device doesn't respond
> > despite being a standard phy. If the parent hardware
> > is capable, it makes sense to scan for c22 devices before
> > falling back to c45.
> > 
> > As we want this to reflect the capabilities of the STA,
> > lets add a field to the mii_bus structure to represent
> > the capability. That way devices can opt into the extended
> > scanning. Existing users should continue to default to c22
> > only scanning as long as they are zero'ing the structure
> > before use.
> > 
> > Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> > Signed-off-by: Calvin Johnson <calvin.johnson@....nxp.com>
> 
> I know that we've hashed this out quite a bit already, but I would like
> to point out that include/linux/mdio.h contains:
> 
>  * struct mdio_if_info - Ethernet controller MDIO interface
>  * @mode_support: MDIO modes supported.  If %MDIO_SUPPORTS_C22 is set then
>  *      MII register access will be passed through with @devad =
>  *      %MDIO_DEVAD_NONE.  If %MDIO_EMULATE_C22 is set then access to
>  *      commonly used clause 22 registers will be translated into
>  *      clause 45 registers.
> 
> #define MDIO_SUPPORTS_C22               1
> #define MDIO_SUPPORTS_C45               2
> #define MDIO_EMULATE_C22                4
> 
> While this structure is not applicable to phylib or mii_bus, it may be
> worth considering that there already exist definitions for identifying
> the properties of the underlying bus.

Can we reuse these or go ahead with the new MDIOBUS_C22?

> 
> > ---
> > 
> >  drivers/net/phy/mdio_bus.c | 17 +++++++++++++++--
> >  include/linux/phy.h        |  7 +++++++
> >  2 files changed, 22 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> > index 6ceee82b2839..e6c179b89907 100644
> > --- a/drivers/net/phy/mdio_bus.c
> > +++ b/drivers/net/phy/mdio_bus.c
> > @@ -739,10 +739,23 @@ EXPORT_SYMBOL(mdiobus_free);
> >   */
> >  struct phy_device *mdiobus_scan(struct mii_bus *bus, int addr)
> >  {
> > -	struct phy_device *phydev;
> > +	struct phy_device *phydev = ERR_PTR(-ENODEV);
> >  	int err;
> >  
> > -	phydev = get_phy_device(bus, addr, false);
> > +	switch (bus->probe_capabilities) {
> > +	case MDIOBUS_C22:
> > +		phydev = get_phy_device(bus, addr, false);
> > +		break;
> > +	case MDIOBUS_C45:
> > +		phydev = get_phy_device(bus, addr, true);
> > +		break;
> > +	case MDIOBUS_C22_C45:
> > +		phydev = get_phy_device(bus, addr, false);
> > +		if (IS_ERR(phydev))
> > +			phydev = get_phy_device(bus, addr, true);
> > +		break;
> > +	}
> > +
> >  	if (IS_ERR(phydev))
> >  		return phydev;
> >  
> > diff --git a/include/linux/phy.h b/include/linux/phy.h
> > index 9248dd2ce4ca..50e5312b2304 100644
> > --- a/include/linux/phy.h
> > +++ b/include/linux/phy.h
> > @@ -298,6 +298,13 @@ struct mii_bus {
> >  	/* RESET GPIO descriptor pointer */
> >  	struct gpio_desc *reset_gpiod;
> >  
> > +	/* bus capabilities, used for probing */
> > +	enum {
> > +		MDIOBUS_C22 = 0,
> > +		MDIOBUS_C45,
> > +		MDIOBUS_C22_C45,
> > +	} probe_capabilities;
> 
> I think it would be better to reserve "0" to mean that no capabilities
> have been declared.  We hae the situation where we have mii_bus that
> exist which do support C45, but as they stand, probe_capabilities will
> be zero, and with your definitions above, that means MDIOBUS_C22.
> 
> It seems this could lock in some potential issues later down the line
> if we want to use this elsewhere.

I'll change it to :

enum {
	MDIOBUS_C22 = 1,
	MDIOBUS_C45,
	MDIOBUS_C22_C45,
} probe_capabilities;

Thanks
Calvin