netdev - RE: [PATCH] net: via-rhine: fix compiler warning

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Date:	Wed, 30 Apr 2014 09:57:40 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Jan Moskyto Matejka' <mq@...e.cz>,
	Alexey Charkov <alchark@...il.com>
CC:	Roger Luethi <rl@...lgate.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net: via-rhine: fix compiler warning

From: Jan Moskyto Matejka
> > > So why not just:
> > >         revision = (unsigned long)match->data;
> > > and add a comment that the 0x84 is the revision - #define ??
> >
> > There is no particular reason why it should be u32 now - this is a
> > leftover from the previous iteration of code where revision was a
> > separate property in DT (sized u32). It actually mirrors the
> > respective field in struct pci_dev, which is u8 - don't see any issue
> > defining it as unsigned long (and also changing the definition in
> > struct rhine_private).
> >
> > The comment that it's the revision is right above the match table (cut
> > off in the patch) :)
> >
> > Jan, would you prefer to adjust your patch, or shall I send another
> > one to change rp->revision and friends to unsigned long?
> 
> I prefer you to make another patch, you obviously know more about this
> driver. Also thanks for suggesting (void*)->(unsigned long), I didn't
> know that these two are defined to have the same size (in kernel code).

The kernel assumes that throughout - the double cast is common.
The C99 type is uintptr_t - but I don't think that is defined in kernel.
The only place I know where sizeof (long) != sizeof (void *) is 64bit
windows. So anyone trying to compile a linux driver to run in the
windows kernel might have issues (never mind the GPL ones).

	David