On 12/30/20 4:07 PM, Ilias Apalodimas wrote:
Add a description of the EFI variables needed to match a Boot####
entry with an initrd.
Signed-off-by: Ilias Apalodimas <[email protected]>
---
doc/uefi/uefi.rst | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/doc/uefi/uefi.rst b/doc/uefi/uefi.rst
index dc930d924022..d8b083ffa708 100644
--- a/doc/uefi/uefi.rst
+++ b/doc/uefi/uefi.rst
@@ -229,6 +229,21 @@ UEFI variables. Booting according to these variables is
possible via::
As of U-Boot v2020.10 UEFI variables cannot be set at runtime. The U-Boot
command 'efidebug' can be used to set the variables.
+Initrd with the boot manager
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Kernel versions >= 5.6 can use EFI_LOAD_FILE2_PROTOCOL to load an initramfs.
%s/can use EFI_LOAD_FILE2_PROTOCOL/can use the Load File 2 protocol/
+When U-Boot is configured with CONFIG_EFI_LOAD_FILE2_INITRD=y the boot manager
+will install the protocol, if an EFI variable matching the BootCurrent value
+is found and contains a valid file path. The EFI variable name is 'Initrd####'
When booting via the UEFI boot manager (command 'bootefi bootmgr')
BootNext and BootOrder are used to identify a boot option to boot. The
variable BootCurrent is set to the hexadecimal number of the selected
boot option, e.g. to 0x001E if the image specified by Boot001E is selected.
When U-Boot is configured with CONFIG_EFI_LOAD_FILE2_INITRD=y the boot
manager will install the Load File 2 protocol if an EFI variable
Initrd#### (e.g. Initrd001E) is found where #### matches the value of
BootCurrent and Initrd#### contains a valid file path.
+and the file path format is '<device> <partition> <filename>'.
The fist string is not a device but a class of devices.
The third string is not a filename but a file path.
<interface> <device>[:<partition>] <filepath>.
partition defaults to 0 (whole disk).
The user should be taught that the value of Initrd#### is a UTF8 string.
An example string should be provided.
+
+This allows users to pair a kernel with a specific initramfs.
+
+Example:
+Boot0010 will search for Initrd0010 and try to install the protocol with
+the file path specified in Initrd0010.
"When booting Boot001E U-Boot tries to install the Load File 2 protocol
with the file specified by Initrd001E. If the intird is not found it
will continue without init.
What happens if Initrd#### does not point to a valid file? Shouldn't we
then skip the boot option and continue with the next boot option?
Please, show how to set Initrd0010 from the console, e.g.
setenv -e -nv -bs -rt Initrd001E 'scsi 0:1 initrd'
Best regards
Heinrich
+
Executing the built in hello world application
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
