netdev - Re: [PATCH RFC V2 2/2] net: qualcomm: new Ethernet over SPI driver for QCA7000

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Message-ID: <20140701181601.GA11399@leverpostej>
Date:	Tue, 1 Jul 2014 19:16:01 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Joe Perches <joe@...ches.com>
Cc:	Stefan Wahren <stefan.wahren@...e.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"f.fainelli@...il.com" <f.fainelli@...il.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"dave.taht@...il.com" <dave.taht@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH RFC V2 2/2] net: qualcomm: new Ethernet over SPI driver
 for QCA7000

On Tue, Jul 01, 2014 at 06:57:45PM +0100, Joe Perches wrote:
> On Tue, 2014-07-01 at 18:46 +0100, Mark Rutland wrote:
> > On Tue, Jul 01, 2014 at 05:36:49PM +0100, Stefan Wahren wrote:
> > > This patch adds the Ethernet over SPI driver for the
> > > Qualcomm QCA7000 HomePlug GreenPHY.
> []
> > > +               memcpy(qca->net_dev->dev_addr, mac, ETH_ALEN);
> > 
> > I believe that it is preferred to write:
> > 
> > 	ether_addr_copy(qca->net_dev->dev_addr, mac);
> > 
> > I believe checkpatch has a warning for this.
> 
> True, but you have to make sure that both args are
> at least __aligned(2) and afaics there's no
> guarantee that's true for mac.

In this case I think there is, though I deleted the context that would
make that clearer. Sorry about that.

We acquired mac with:

	mac = of_get_mac_address(spi_device->dev.of_node);

Where of_get_mac_address returns a property::value pointer.

As far as I can tell, when we unflatten the DT each property::value is
pointed at the original data in the DTB. Each data stream immediately
follows a naturally aligned 32-bit FDT_PROP token in the DTB, so all
value pointers should be aligned to at least 4 bytes.

That all said I'm happy to just use memcpy if we're not happy to rely on
the DTB format, it's not exactly going to be a bottleneck.

Cheers,
Mark.
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