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

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Message-ID: <20328.33660.472382.117901@ipc1.ka-ro>
Date:	Tue, 20 Mar 2012 14:17:48 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Dong Aisheng <dongas86@...il.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Dong Aisheng <aisheng.dong@...escale.com>,
	"vinod.koul\@linux.intel.com" <vinod.koul@...ux.intel.com>,
	"s.hauer\@pengutronix.de" <s.hauer@...gutronix.de>,
	"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>,
	Guo Shawn-R65073 <r65073@...escale.com>,
	"rdunlap\@xenotime.net" <rdunlap@...otime.net>,
	"kernel\@pengutronix.de" <kernel@...gutronix.de>,
	"cjb\@laptop.org" <cjb@...top.org>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"devicetree-discuss\@lists.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.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 Mon, Mar 19, 2012 at 3:02 PM, Grant Likely <grant.likely@...retlab.ca> wrote:
> > On Mon, 19 Mar 2012 17:49:02 +0100, Lothar Waßmann <LW@...O-electronics.de> wrote:
> >> Hi,
> >>
> >> Grant Likely writes:
> >> > On Mon, 19 Mar 2012 07:54:33 +0100, Lothar Waßmann <LW@...O-electronics.de> wrote:
> >> > > Grant Likely writes:
> >> > > > On Fri, 16 Mar 2012 11:01:35 +0800, Dong Aisheng <aisheng.dong@...escale.com> wrote:
> >> > > > > On Thu, Mar 15, 2012 at 07:22:04PM +0800, Lothar Waßmann wrote:
> >> > > > > > Dong Aisheng writes:
> >> > > > > > > On Thu, Mar 15, 2012 at 02:53:29PM +0800, Lothar Waßmann wrote:
> >> > > > > > 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.
> >> > > > > >
> >> > > > > It's just provide one more option since there are customers storing the MAC
> >> > > > > in the fuse map.
> >> > > >
> >> > > > That should be straight forward to support; have a property that
> >> > > > specifies the method used for fetching/calculating the MAC.
> >> > > >
> >> > > Executable code stored inside a DT blob? ;)
> >> >
> >> > I know you're joking here, but I'm going to answer seriously
> >> > anyway... Absolutely not.  What I'm suggesting is a property that
> >> > specifies the method used to determine the mac address.  Something
> >> > like (off the top of my head):
> >> >
> >> >     local-mac-address = [01 02 03 00 00 00];
> >> >     local-mac-mask = [0xff 0xff 0xff 0 0 0];
> >> >     mac-encoding = "append-serial-number";
> >> >
> >> That still does not specify where the remaining part of the MAC is
> >> stored and how it should be retrieved.
> >
> > I'm suggesting that you define a string that means something specific;
> > that hopefully can be shared by multiple platforms.  For example,
> > "append-serial-number" might mean start with the values selected by
> > AND of local-mac-address and local-mac-mask, and OR in the board's
> > serial number.  You would need to define something that worked if this
> > was the solution you used.
> >
> I'm intend to Grant's this suggestion.
> This can be shared by all other imx platforms which stores mac address in
> fuse map and this is commonly used by customer.
> Then we do not need keep writing repeat code for different platforms
> via platform
> data.
> 
> For Lothar's question, we can add a property fuse_mac_offset to indicate
> read mac from fuse map and where to read it.
>
That's not really enough. The format (big-endian vs. little-endian)
may also differ. But it's not really necessary, if the solution with
prom_update_property() works, since then platform code has full
control over the MAC.

> For how many bytes to read, we can calculate it from the local-mac-mask.
> For example, local-mac-mask = [0xff 0xff 0xff 0 0 0], we can get the size
> as 3 bypes.
> 
> Then we have three properties:
> local-mac-address = [01 02 03 00 00 00];
> local-mac-mask = [0xff 0xff 0xff 0 0 0];
> fuse_mac_offset = <1>;
> 
> In fec driver, the final mac address can be got by:
> local-mac-address & local-mac-mask | (read_fuse(1) & 0xffffff)
> 
> Lathar,
> Do you think if this is ok?
>
No. IMO the FEC driver itself should not read any fuses.
Reading fuses is a SoC specific thing and the FEC driver should not
depend on the idiosyncrasies of some SoC wrt. anything else but the
implementation of the FEC itself.


Lothar Waßmann
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