On 17.10.23 11:14, Ilias Apalodimas wrote:
Hi Heinrich,
On Tue, 17 Oct 2023 at 11:55, Heinrich Schuchardt
<heinrich.schucha...@canonical.com
<mailto: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.
Signed-off-by: Heinrich Schuchardt
<heinrich.schucha...@canonical.com
<mailto:heinrich.schucha...@canonical.com>>
---
lib/efi_loader/efi_setup.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c
index e6de685e87..b24feb94dc 100644
--- a/lib/efi_loader/efi_setup.c
+++ b/lib/efi_loader/efi_setup.c
@@ -26,6 +26,27 @@ void __weak allow_unaligned(void)
{
}
+/**
+ * efi_init_fdtfile() - set EFI variable FdtFile
+ *
+ * Return: status code
+ */
+static efi_status_t efi_init_fdtfile(void)
+{
+ char *val;
+
+ val = env_get("fdtfile");
+ if (!val)
+ return EFI_SUCCESS;
+
+ return efi_set_variable_int(u"FdtFile",
+ &efi_u_boot_guid,
+ EFI_VARIABLE_BOOTSERVICE_ACCESS |
+ EFI_VARIABLE_RUNTIME_ACCESS |
Why is runtime access needed? Wouldn't the choice be done before
ExitBootServices?
Having runtime access will allow to use the content of the variable to
write a devicetree command to grub.cfg or to copy the relevant
device-tree to a predefined location.
As GRUB cannot read EFI variables, yet, this would be the easiest
short-term approach.
Best regards
Heinrich
[...]
Thanks
/Ilias
