[U-Boot] [PATCH] x86: Add a pointer to the global data structure to point to the device tree

[Gabe Black]

On Mon, Dec 5, 2011 at 5:49 PM, Graeme Russ <graeme.russ at gmail.com> wrote:

> Hi Gabe,
>
> On Tue, Dec 6, 2011 at 12:43 PM, Gabe Black <gabeblack at chromium.org>
> wrote:
> > This change adds a pointer to the global data structure in x86 to point
> to
> > the device tree. This mirrors an identical pointer in ARM.
>
> Out of curiosity, is this paving the way for FDT support in general?
> If so, to what extent does the Linux kernel support FDT for x86?
>
> I have had thoughts about looking into what Device Tree / FDT is all
> about, and I'm wondering what it is going to bring to the table
> (positive and negative) for x86. For example, would this, in theory,
> depricate the boot_params structure, e820 map etc...
>
> Regards,
>
> Graeme
>


The device tree can be used in two different ways, by u-boot and by the
kernel. This is for use by u-boot itself and is one mechanism coreboot can
use to make its own runtime modification to how u-boot is set up (if
there's a serial console it can use, for instance), and it is fairly
useful. The kernel has some very minimal provisions for passing in a device
tree in x86 through, if I remember correctly, basically a linked list of
entries which hang off the end of the boot_params structure. The kernel
doesn't take advantage of it at all, so it wouldn't really be useful to
pass one in. There are times when it would be a good solution to certain
problems but the kernel would have to actually be set up to take advantage
of it first.

Gabe