linux-kernel - Re: [PATCH v1 1/5] ARM: imx28: add basic dt support

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Message-ID: <20321.53468.310199.875966@ipc1.ka-ro>
Date:	Thu, 15 Mar 2012 12:22:04 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Dong Aisheng <aisheng.dong@...escale.com>
Cc:	Dong Aisheng-B29396 <B29396@...escale.com>,
	"s.hauer\@pengutronix.de" <s.hauer@...gutronix.de>,
	Guo Shawn-R65073 <r65073@...escale.com>,
	"vinod.koul\@linux.intel.com" <vinod.koul@...ux.intel.com>,
	"devicetree-discuss\@lists.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-mmc\@vger.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring\@calxeda.com" <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	"rdunlap\@xenotime.net" <rdunlap@...otime.net>,
	"kernel\@pengutronix.de" <kernel@...gutronix.de>,
	"cjb\@laptop.org" <cjb@...top.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1 1/5] ARM: imx28: add basic dt support

Hi,

Dong Aisheng writes:
> On Thu, Mar 15, 2012 at 02:53:29PM +0800, Lothar Waßmann wrote:
> > Hi,
> > 
> > Dong Aisheng writes:
> > > On Wed, Mar 14, 2012 at 10:16:43PM +0800, s.hauer@...gutronix.de wrote:
> > > > On Wed, Mar 14, 2012 at 08:45:23PM +0800, Dong Aisheng wrote:
> > > > > On Wed, Mar 14, 2012 at 01:23:51AM +0800, Grant Likely wrote:
> > [...]
> > > > > But it seems this needs pass mac address to fec driver via platforom data which is
> > > > > not friendly to dt.
> > > > > 
> > > > > Another way may be changing fec driver to get the fixed part of mac address(first
> > > > > two bytes) from device tree and read the left dynamical part from otp which i'm not
> > > > > sure is better enough.
> > > > > 
> > > > > BTW, filling with zeros seems not work since it's invalid mac address.
> > > > 
> > > > Yes, that's the idea of using this value...
> > > > 
> > > But comparing to use an invalid value, why not just do not define that
> > > local-mac-address property?
> > > 
> > Because a MAC address is by definition a GLOBALLY UNIQUE IDENTIFIER
> > which is contrary to coding a "valid" default value for it somewhere!
> > The owner of a certain MAC address range (OUI) is responsible for
> > ensuring the uniqueness. Thus only they may assign a specific MAC
> > address to a specific device.
> > 
> Yes, you're correct.
> So i propose to read the MAC address from MX28 OTP in fec driver instead of
> define it in device tree in my last mail.
> http://www.spinics.net/lists/arm-kernel/msg165040.html
> Do you have any comment on that way?
> 
That patch sets the OUI to the Freescale owned MAC range. Thus only
Freescale products may be able to use the driver.

Anyway there is no definite spec how the MAC address(es) are stored
in the fuse map. Thus reading the MAC from there is more or less
platform specific.

Currently I'm setting up the MAC address for our TX28 from the fuses
in the platform code passed via platform_data, but that will obviously
not work with DT.

The correct way would probably be to pass the MAC from the bootloader
via a DT blob. But that would require all bootloaders to be updated
first to support DTS. :(

An intermediate solution could be using OF_DEV_AUXDATA to pass a
platform_data struct that may contain a MAC address set up by the
platform code.


Lothar Waßmann
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