netdev - Re: [PATCH V2 3/3] ethernet: Convert mac address uses of 6 to ETH

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Message-ID: <1375391087.2034.82.camel@joe-AO722>
Date:	Thu, 01 Aug 2013 14:04:47 -0700
From:	Joe Perches <joe@...ches.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	David Miller <davem@...emloft.net>
Cc:	Olof Johansson <olof@...om.net>, Sam Creasey <sammy@...my.net>,
	Grant Grundler <grundler@...isc-linux.org>,
	Wan ZongShun <mcuos.com@...il.com>,
	Rajesh Borundia <rajesh.borundia@...gic.com>,
	Network Development <netdev@...r.kernel.org>,
	Sony Chacko <sony.chacko@...gic.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Manish Chopra <manish.chopra@...gic.com>,
	Don Fry <pcnet32@...ntier.com>,
	Ron Mercer <ron.mercer@...gic.com>,
	Andrew Gallatin <gallatin@...i.com>, linux-driver@...gic.com,
	Jitendra Kalsaria <jitendra.kalsaria@...gic.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Shahed Shaikh <shahed.shaikh@...gic.com>
Subject: Re: [PATCH V2 3/3] ethernet: Convert mac address uses of 6 to
 ETH_ALEN

On Thu, 2013-08-01 at 21:58 +0100, Russell King - ARM Linux wrote:
> On Thu, Aug 01, 2013 at 01:55:28PM -0700, Joe Perches wrote:
> > On Thu, 2013-08-01 at 21:33 +0100, Russell King - ARM Linux wrote:
> > > On Thu, Aug 01, 2013 at 01:31:09PM -0700, Olof Johansson wrote:
> > > > On Thu, Aug 1, 2013 at 1:14 PM, Joe Perches <joe@...ches.com> wrote:
> > > > > diff --git a/drivers/net/ethernet/pasemi/pasemi_mac.h b/drivers/net/ethernet/pasemi/pasemi_mac.h
> > []
> > > > > @@ -79,11 +79,11 @@ struct pasemi_mac {
> > > > >         int             last_cs;
> > > > >         int             num_cs;
> > > > >         u32             dma_if;
> > > > > -       u8              type;
> > > > >  #define MAC_TYPE_GMAC  1
> > > > >  #define MAC_TYPE_XAUI  2
> > > > >
> > > > > -       u8              mac_addr[6];
> > > > > +       u8              mac_addr[ETH_ALEN];
> > > > > +       u8              type;
> > > > 
> > > > Just promote 'type' to u32 instead, saves you from moving the #defines
> > > > down, etc, etc.
> > 
> > type is already u8, why change it?
> > That would also change struct size.
> > 
> > > There's a more fundamental question which has to be asked: what is the
> > > point of moving that in the first place?
> > 
> > Some is_<foo>_ether_addr tests assume __aligned(2)
> > by a casting char * to u16/be16 * and dereferencing.
> > 
> > see patch 0/3 and include/linux/etherdevice.h
> 
> This seems rather obscure - I mean, it's not obvious to driver authors
> that should be the case.  Would it not be better to make this a little
> more obvious somehow?  Maybe __aligned(2) against mac_addr?  Or
> maybe have a debugging check for it?

That'd be for David Miller (cc'd).

I believe he's argued in the past that any alignment check
for mac addresses was unnecessary.

For all I know it really might not matter because pasemi
can successfully dereference a ushort against an odd char
pointer.

I just noticed it and thought it'd be better moved.


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