Re: [PATCH v2] net: Add eth_platform_get_mac_address() helper.

[David Miller <davem@davemloft.net>]

From: Joe Perches <joe@perches.com>
Date: Wed, 06 Jan 2016 15:32:24 -0800

> On Thu, 2016-01-07 at 00:26 +0100, Bjørn Mork wrote:
>> Joe Perches <joe@perches.com> writes:
>> > On Wed, 2016-01-06 at 16:33 -0500, David Miller wrote:
>> > > A repeating pattern in drivers has become to use OF node information
>> > > and, if not found, platform specific host information to extract the
>> > > ethernet address for a given device.
>> > []
>> > > diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
>> > []
>> > > @@ -485,3 +487,32 @@ static int __init eth_offload_init(void)
>> > >  }
>> > >  
>> > >  fs_initcall(eth_offload_init);
>> > > +
>> > > +unsigned char * __weak arch_get_platform_mac_address(void)
>> > > +{
>> > > +       return NULL;
>> > 
>> > WARN_ON_ONCE ?
>> 
>> That would prevent a driver from using this with additional fallback
>> methods.  For what reason?
> 
> It's declared __weak and should be overridden by
> an arch specific function.
> 
> A NULL address would cause a fault when using
> a function like copy_ether_addr.

The caller checks for NULL, and this is the default implementation
doing precisely what it is meant to do.