On Mon, Jul 07, 2008 at 11:28:43AM +1000, David Gibson wrote:

quoted

This function is surely needed in every case I considered so far. I am
just sceptical if the boot-loader can determine a correct parentoffset
all alone (which one of the two I2C busses is the correct one?). This is

Hrm.  "all alone".  It's not clear to me what else there could be that
would have more information than the bootloader.

What I meant is that all the information a bootloader has may not be
sufficent. To solve this, some additional infos could be added to the
tree. In this case, it could be a few aliases.

quoted

What I encoded using "external-name" is where possible fragments
_could_ be added to. Something like a mount-point. The boot-loader
decides if and what could be mounted there. As an "/aliases" node is
already in use, I would favour to add such mount-points there.

Hrm.  I'm not convinced that the mount point model is actually a good
one.  I would have thought that one of the most common things to graft
would be extra optional devices onto a bus.  In this case there's no
specific "mountpoint"  the device could be attached at any valid
address on the bus in question.

Maybe I am really missing something here, but what is the bus in
question? How do you tell from such an entry

rtc@51{
	device_type="rtc";
	compatible="nxp,pcf8563";
	reg=<0x51>;
};

if it is connected to "/pci/pci_bridge/isa" as in mpc8548cds.dts or to
"/soc5200/i2c@3d40" as in pcm030.dts? The latter even has another
I2C-bus i2c@3d00 which could also be a possibility. This is why I'd like
to encode the fragment as:

i2c_0 {
	rtc@51{
		device_type="rtc";
		compatible="nxp,pcf8563";
		reg=<0x51>;
	};
};

with i2c_0 being an alias to the proper bus. Maybe I should add that I
am _not_ assuming that the fragment is obtained from the bus which wants to
have devices added. That is, one I2C-eeprom may contain data about
additional devices on PCI.

Kind regards,

   Wolfram

-- 
  Dipl.-Ing. Wolfram Sang | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry