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The device-tree built into U-Boot is often out of date and not usable to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.
Best regards
Heinrich
