Re: [Qemu-devel] [PATCH] arm: add device tree support

[John Williams]

On Mon, Jan 30, 2012 at 5:13 AM, Peter Maydell <address@hidden> wrote:
> On 29 January 2012 16:01, Grant Likely <address@hidden> wrote:
>> On Sun, Jan 29, 2012 at 11:15:42AM +0000, Paul Brook wrote:
>>> Clearly we need to have some sort of FDT support.  However I'm unconvinced
>>> that it's the correct format for the primary data structure.  For one thing
>>> it's a hierarchical tree structure, and in my experience describing links
>>> outside that structure gets hairy.  One of the things we're doing with QOM 
>>> is
>>> move from a hierarchical tree/bus to a more general connected web of links
>>> between devices.
>>
>> Okay, well at least let's start with this.  Here is an updated version of the
>> patch that doesn't touch the board code.  It makes the -dtb option available
>> to all ARM platforms.
>>
>> Even if dtb is not the primary structure, we absolutely need this option.
>> Developers using qemu to simulate real hardware are going to still want
>> to pass in the exact same .dtb file to qemu as they use for the real target,
>> and those .dtb files are maintained completely separately from qemu.
>
> I agree with Paul that trying to use the dtb as the primary structure
> for describing a machine model to qemu is decidedly problematic. Let's
> start with the basic "we're a bootloader, provide minimal support for
> passing in a device tree blob"...

We've never advocated DTB as primary structure, but rather just one
very useful, simple and generic approach.

Among the the sea of fixed machine models that is QEMU today, having a
DTB-driven machine in there would be an excellent proving ground for
QOM conversion and steps towards fully data driven machines which
should be the ultimate objective anyway.

As Peter C says elsewhere in this thread, through its link syntax
foo=<&ref> you can describe any sort of topology you like in a device
tree.

Regards,

John
-- 
John Williams, PhD, B. Eng, B. IT
PetaLogix - Linux Solutions for a Reconfigurable World
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