RE: Device tree support for x86 on Linux

[Mislav Stublić]

Hi Daniel,

Regarding reusing existing code, there is grub-core/loader/efi/fdt.c which 
atleast  df s a f

-----Original Message-----
From: Daniel Kiper [mailto:dkiper@net-space.pl]
Sent: Friday, July 30, 2021 2:59 PM
To: Mislav Stublić
Cc: grub-devel@gnu.org
Subject: Re: Device tree support for x86 on Linux

Hi Mislav,

On Thu, Jul 29, 2021 at 08:43:45AM +0000, Mislav Stublić wrote:
> Hi,
>
> I am planning to add support for device tree loading on x86 with UEFI
> and Linux as i understand this is currently not supported. We need
> this for a board we are developing so i would test my patches in our
> development environment.
>
> I have gone through current x86 loader code and some similar use cases
> so i  believe i could provide a patch but i also have some questions.
>
> Is this a feature you would accept upstream?

I do not see any issues with it. It would be nice if you could reuse existing 
code as much as possible. And please remember that current GRUB code does not 
allow you to load device tree files if UEFI Secure Boot is enabled. You can 
find more info here: grub-core/kern/lockdown.c.

> As for technical questions, for this to work grub would need to set
> setup_data pointer (part of setup_header for linux kernel) that points
> to memory holding loaded dtb. But i'm not sure if such memory can just
> be allocated with grub_zalloc or is there some other allocation

The grub_zalloc() et consortes can be used for the GRUB "runtime" only.

> mechanism that would guarantee this will be preserved once control is
> handed over to linux kernel.

There are two functions in the GRUB which are doing what you want:
grub_relocator_alloc_chunk_align() and grub_relocator_alloc_chunk_addr().
It seems to me the former should be better for you.

Daniel


----- Disclaimer -----
This e-mail message and its attachments may contain privileged and/or 
confidential information. Please do not read the message if You are not its 
designated recipient. If You have received this message by mistake, please 
inform its sender and destroy the original message and its attachments without 
reading or storing of any kind. Any unauthorized use, distribution, 
reproduction or publication of this message is forbidden.

----- Pravne napomene -----
Ova elektronicka poruka i njeni prilozi mogu sadrzavati povlastene informacije 
i/ili povjerljive informacije. Molimo Vas da poruku ne citate ako niste njen 
naznaceni primatelj. Ako ste ovu poruku primili greskom, molimo Vas da o tome 
obavijestite posiljatelja i da izvornu poruku i njene privitke unistite bez 
citanja ili bilo kakvog pohranjivanja. Svaka neovlastena upotreba, 
distribucija, reprodukcija ili priopcavanje ove poruke zabranjena je.