On Thu, 19 May 2005, Benjamin Herrenschmidt wrote:
Here's the very first draft of my HOWTO about booting the linux/ppc64 kernel without open firmware. It's still incomplete, the main chapter
^^^^^^^^^^^^^^^^^^^^^One could argue whether the full-blown emulation of an OF device tree may really be called this.... ;-)
You must be kidding :)
Honestly, a device tree is small and rather simple to layout, and would fix most of the issues with piling up crap like incompatible boot_info structures and that sort of thing that plague the ppc32 kernel.
Yes, I know, and I *was* kidding. :-) What I was trying to hint, at, really, was that there is just a bit more than resemblance to what real OF based systems will provide for a device tree. And rightly so, no need to it difficult for those.
For OF based systems, what you outline definitely makes an awful lot of sense.
How so ? OF based system just implement the OF interface...
Er, yes, and that is why it makes sense to design it that way. Maybe striking out the word "awful" makes my statement clearer :-)
Regarding the cost, well, the device-tree itself is fairly small, maybe a couple of pages for a minimum one. As I wrote, embedded boards can
Without knowing the size of the code required for this, it would still mean an increase by a couple of hundred percent for the boot information.
I wonder sometimes why people are so "afraid" of the device-tree concept... it's really simple, does not require that much code, and makes everything so much more flexible in the long run.
Oh, don't get me wrong: I'm not against the device tree per se, I was just pondering a little on your draft, according to the "RFC" bit in the subject. Actually I welcome your efforts a lot, since I, too, suffered from the mess we a currently in. So, by all means, please do go on!
Cheers, Marius