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

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Message-ID: <51A399D6.8030000@free-electrons.com>
Date:	Mon, 27 May 2013 19:37:26 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
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 27/05/2013 18:39, Sascha Hauer wrote:
> 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.

Right, I tried that first but forgot static so I had issues with
redefinition of the functions. I even played with __weak at some point...

I'll wait a bit for comments before sending v2.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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