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

[Graeme Russ]

Hi Gabe,

On Tue, Dec 6, 2011 at 1:04 PM, Gabe Black <gabeblack at chromium.org> wrote:
>
>
> 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

I thought this list was just a linked list of more e820 entries (and that is
what the code seems to suggest)

> 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.

Does UEFI support device trees? If so, I wonder if this is the future of
Linux and x86 support is somewhat inevitable?

Regards,

Graeme