linux-kernel - Re: [PATCH 1/3] net: phy: prevent linking breakage

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Date:	Mon, 27 May 2013 18:39:13 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	Shawn Guo <shawn.guo@...aro.org>,
	Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH 1/3] net: phy: prevent linking breakage

On Mon, May 27, 2013 at 06:18:42PM +0200, Alexandre Belloni wrote:
> phy_register_fixup{,_for_uid,_for_id} are called from arch/, quite
> often, there is no protection to check whether CONFIG_PHYLIB=y which is
> the only case where this would work. Having phylib as a module or not
> compiled at all will result in that kind of linking failure:
> 
> arch/arm/mach-at91/built-in.o: In function `ksz9021rn_phy_fixup':
> :(.text+0x1174): undefined reference to `mdiobus_write'
> :(.text+0x1188): undefined reference to `mdiobus_write'
> :(.text+0x119c): undefined reference to `mdiobus_write'
> :(.text+0x11b0): undefined reference to `mdiobus_write'
> arch/arm/mach-at91/built-in.o: In function `sama5_dt_device_init':
> :(.init.text+0x1e34): undefined reference to `phy_register_fixup_for_uid'
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> ---
>  drivers/net/phy/phy_device.c |  6 ++++++
>  include/linux/phy.h          | 12 ++++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 3657b4a..df36367 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -64,6 +64,11 @@ static int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>  			     u32 flags, phy_interface_t interface);
>  
>  /*
> + *  phy_register_fixup{,_for_uid,_for_id} are called from arch/ so this won't
> + *  work unless phylib is compiled in the kernel.
> + */
> +#ifdef CONFIG_PHYLIB
> +/*
>   * Creates a new phy_fixup and adds it to the list
>   * @bus_id: A string which matches phydev->dev.bus_id (or PHY_ANY_ID)
>   * @phy_uid: Used to match against phydev->phy_id (the UID of the PHY)
> @@ -109,6 +114,7 @@ int phy_register_fixup_for_id(const char *bus_id,
>  	return phy_register_fixup(bus_id, PHY_ANY_UID, 0xffffffff, run);
>  }
>  EXPORT_SYMBOL(phy_register_fixup_for_id);
> +#endif /* CONFIG_PHYLIB */
>  
>  /*
>   * Returns 1 if fixup matches phydev in bus_id and phy_uid.
> diff --git a/include/linux/phy.h b/include/linux/phy.h
> index 9e11039..3f998a6 100644
> --- a/include/linux/phy.h
> +++ b/include/linux/phy.h
> @@ -556,12 +556,24 @@ int phy_start_interrupts(struct phy_device *phydev);
>  void phy_print_status(struct phy_device *phydev);
>  void phy_device_free(struct phy_device *phydev);
>  
> +/*
> + *  phy_register_fixup{,_for_uid,_for_id} are called from arch/ so this won't
> + *  work unless phylib is compiled in the kernel.
> + *  Defining stubs allows to prevent linking errors.
> + */
> +#ifdef CONFIG_PHYLIB
>  int phy_register_fixup(const char *bus_id, u32 phy_uid, u32 phy_uid_mask,
>  		int (*run)(struct phy_device *));
>  int phy_register_fixup_for_id(const char *bus_id,
>  		int (*run)(struct phy_device *));
>  int phy_register_fixup_for_uid(u32 phy_uid, u32 phy_uid_mask,
>  		int (*run)(struct phy_device *));
> +#else
> +#define phy_register_fixup(a, b, c, d) do { } while (0)
> +#define phy_register_fixup_for_id(a, b) do { } while (0)
> +#define phy_register_fixup_for_uid(a, b, c) do { } while (0)

Use static inline functions here. This breaks if someone does result
checking on the functions which then expands to ret = do {} while (0);
Also we still have type safety for !CONFIG_PHYLIB.

Sascha

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