netdev - Re: [PATCH 1/5] phylib: don't return NULL from get_phy

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Date:	Thu, 28 Apr 2016 00:03:38 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	Andrew Lunn <andrew@...n.ch>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	"David S. Miller" <davem@...emloft.net>, f.fainelli@...il.com,
	netdev@...r.kernel.org, kernel@...oirfairelinux.com
Subject: Re: [PATCH 1/5] phylib: don't return NULL from get_phy_device()

On Wednesday 27 April 2016 23:09:37 Sergei Shtylyov wrote:
> Hello.
> 
> On 04/27/2016 10:49 PM, Andrew Lunn wrote:
> 
> >> Sergei Shtylyov <sergei.shtylyov@...entembedded.com> writes:
> >>
> >>> Arnd Bergmann asked that get_phy_device() returns either NULL or the error
> >>> value,  not both on error.  Do as he said, return ERR_PTR(-ENODEV) instead
> >>> of NULL when the PHY ID registers read as  all ones.
> >>>
> >>> Suggested-by: Arnd Bergmann <arnd@...db.de>
> >>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> >>>
> >>> ---
> >>>   drivers/net/phy/phy_device.c |    2 +-
> >>>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> Index: net-next/drivers/net/phy/phy_device.c
> >>> ===================================================================
> >>> --- net-next.orig/drivers/net/phy/phy_device.c
> >>> +++ net-next/drivers/net/phy/phy_device.c
> >>> @@ -529,7 +529,7 @@ struct phy_device *get_phy_device(struct
> >>>
> >>>   	/* If the phy_id is mostly Fs, there is no device there */
> >>>   	if ((phy_id & 0x1fffffff) == 0x1fffffff)
> >>> -		return NULL;
> >>> +		return ERR_PTR(-ENODEV);
> >>>
> >>>   	return phy_device_create(bus, addr, phy_id, is_c45, &c45_ids);
> >>>   }
> >
> > This change is wrong, it needs reverting, or the call sights need
> > fixing to expect ENODEV.
> 
>     So this function had a good reason to return NULL, as it turned out... :-(
> 
> > The point is, the device not being there is not an error, with respect
> > to the code calling this function.
> >
> > It gets called by mdiobus_scan()
> >
> > struct phy_device *mdiobus_scan(struct mii_bus *bus, int addr)
> > {
> >          struct phy_device *phydev;
> >          int err;
> >
> >          phydev = get_phy_device(bus, addr, false);
> >          if (IS_ERR(phydev) || phydev == NULL)
> >                  return phydev;
> >
> > So before, we return NULL, if the device was not there. Now we return
> > ERR_PTR(-ENODEV).
> >
> > This is being called by:
> >
> > int __mdiobus_register(struct mii_bus *bus, struct module *owner)
> > {
> >          struct mdio_device *mdiodev;
> > ...
> >          for (i = 0; i < PHY_MAX_ADDR; i++) {
> >                  if ((bus->phy_mask & (1 << i)) == 0) {
> >                          struct phy_device *phydev;
> >
> >                          phydev = mdiobus_scan(bus, i);
> >                          if (IS_ERR(phydev)) {
> >                                  err = PTR_ERR(phydev);
> >                                  goto error;
> >                          }
> >                  }
> >          }
> >
> > This is treating ERR_PTR(-ENODEV) as a fatal error, where as before
> > IS_ERR(NULL) would be false and it would continue scanning other
> > addresses on the bus.
> 
>     Thank you for the detailed analysis! (And shame on me for the lack of it.)
> 
> > Please revert this, or fix all the callsites such that ENODEV is not a
> > fatal error.
> 
>     OK, I'll do what DaveM decides.

I found one other user that remains broken: pxa168_init_phy() looks 
wrong before and after the patch:

        pep->phy = mdiobus_scan(pep->smi_bus, pep->phy_addr);
        if (!pep->phy)
                return -ENODEV;

        err = phy_connect_direct(dev, pep->phy, pxa168_eth_adjust_link,
                                 pep->phy_intf);

as phy_connect_direct() will go on and dereference an error pointer. This
should check for IS_ERR(), and with the patches applied, we can drop the
!pep->phy check.

	Arnd