[RFC] consolidated libdt proposal

Pantelis Antoniou pantelis at embeddedalley.com
Tue Aug 8 19:34:01 EST 2006

On 08 Αυγ 2006, at 8:37 ΠΜ, Haren Myneni wrote:

> Hollis Blanchard wrote:
>> On Sun, 2006-08-06 at 19:38 -0500, Hollis Blanchard wrote:
>>> Hmm, so we'll have at least three copies of this code: uboot,  
>>> kernel,
>>> and Xen. Would it make sense to put this stuff into a libdt.a?
>>> Technically, dtc has a "libdt" already, but it's absurdly incomplete
>>> (I don't even know why it's there), so we could just replace it.
>> Mark, I had a look at the code Pantelis wrote for u-boot, and it was
>> pretty easy to adapt to meet Xen's (userspace-based) needs. I've
>> attached my version below (and see ft_setup() at the bottom of the
>> file). Does it meet your requirements for the kernel bootwrapper?
>> One limitation of the attached code is that it doesn't support  
>> changing
>> the *size* of properties, though I don't think that would be too
>> difficult to add if needed.
>> Haren, what about using this in kexec-tools?
> Hollis,
>    Good idea to have this lib. Based on brief look, some of these  
> funcs are also useful for kexec-tools. Yes, as you mentioned,  
> changing the size of properties is important for kexec/kdump.
> Present flattened device-tree process in kexec-tools:
> - Kexec-tool reads the /proc/device-tree and sort these entries  
> since we get the different order than the first kernel uses.
> - creates linux,usable-memory property under /proc/device-tree/ 
> memory@* as appropriate.  (for kdump)
> - Modify the reserve map for RTAS, initrd, TCE and (0- crashkernel- 
> start)
> - Create initrd properties if not exist in the first kernel as needed
> - Modify bootargs property
> Thanks
> Haren

Hi Haren,

Mind writing down what your requirements are? Just modifying the size  
of the properties?

Note that my functions work in a two phases.
In the first phase the tree is build with the string table being put  
at the end
of the allocated memory area in a downward motion.
When the tree is finalized the string table is memmov'ed to be  
adjacent to the structure

Could you use this two phased approach for you uses? I.e. first work  
with maximum sized
properties and perform a move & fixup stage when finalizing?



>> If everybody can use this (I expect small modifications would be
>> needed), I think we should turn it into a library in the dtc source
>> tree. The various projects using it could then include snapshots (to
>> avoid dependencies). In general I'd like to avoid everybody  
>> writing and
>> maintaining their own version of this stuff (myself included).
>> --------------------------------------------------------------------- 
>> ---
>> /

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