Hi Heinrich,
On Wed, 18 Oct 2023 at 02:15, Heinrich Schuchardt heinrich.schuchardt@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.schuchardt@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.schuchardt@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The device-tree built into U-Boot is often out of date and not usable to boot current Linux.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.
Also, can we test this interface?
Regards, Simon