On 19.10.23 15:55, Simon Glass wrote:
Hi Heinrich,
On Wed, 18 Oct 2023 at 02:15, Heinrich Schuchardt
<heinrich.schucha...@canonical.com> wrote:
On 10/18/23 05:33, Simon Glass wrote:
Hi Heinrich,
On Tue, 17 Oct 2023 at 07:50, Heinrich Schuchardt
<heinrich.schucha...@canonical.com> wrote:
Forward and backward compatibility of Linux kernel device-trees is
sometimes missing. One solution approach is to load a kernel specific
device-tree. This can either be done via a U-Boot scripts (like the one
generated by Debian package flash-kernel or by a boot loader like GRUB.
The boot loader approach currently requires to know the device-tree name
before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile.
This will allow bootloaders to load a kernel specific device-tree.
The variable will not be exposed on ACPI based systems or if the
environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
---
v2:
Use a unique GUID to enable future U-Boot independent
standardization.
Do not try to add the variable on ACPI based systems.
---
include/efi_loader.h | 5 +++++
lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
I was too slow to reply to v1.
Does grub load the DT? I was assuming that U-Boot would pass it on?
What is the interface between U-Boot and grub?
The device-tree built into U-Boot is often out of date and not usable to
boot current Linux. A single device-tree can be loaded by U-Boot from
file and passed on as EFI configuration table. This device-tree may not
be compatible with all kernel versions exposed by GRUB.
GRUB provides a devicetree command. It is disabled if you use secure
boot. At least in Debian and Ubuntu GRUB invokes the
EFI_DT_FIXUP_PROTOCOL exposed by U-Boot to run U-Boot's device-tree
fix-ups after loading a device-tree.
Vendor scripts for GRUB like Ubuntu's /etc/grub.d/10_linux add
devicetree commands to the boot options in grub.cfg.
Thanks. I wonder if you could document this somewhere? It seems like
there are a lot of options and it is quite complicated.
Back to the question, I suppose you are expecting grub to load the DT
using this filename? But why doesn't U-Boot load it instead? It seems
very convoluted.
A separate file of this name exists for every kernel version installed.
The loaded dtb must match the kernel. U-Boot does not know what kernel
version will be chosen in GRUB. And for a generic image GRUB does not
what board it is on.
Also, can we test this interface?
Neither the sandbox nor QEMU have environment variable fdtfile. And we
don't create the EFI variable with ACPI as used on the sandbox.
Best regards
Heinrich
