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docs(arm): enable Linux boot from fip as BL33

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Document additional functionality of TF-A to package the Linux kernel in
the fip image as a BL33 and boot it. A ramdisk is used as a file system.
The ramdisk properties are injected in to the device tree at build time.

Change-Id: I326f920fdac4bd20572f6f0da07d012def114274
Signed-off-by: Salman Nabi <salman.nabi@arm.com>
This commit is contained in:
Salman Nabi 2024-12-18 15:52:16 +00:00
parent eb8cb9534b
commit 2de9a254c8
1 changed files with 51 additions and 25 deletions
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76
docs/plat/arm/fvp/fvp-specific-configs.rst
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@ -73,13 +73,60 @@ used:
The address provided to the FVP must match the ``EL3_PAYLOAD_BASE`` address
used when building TF-A.
Booting a preloaded kernel image
--------------------------------
Booting a kernel image in BL33
------------------------------
TF-A can boot a Linux kernel, which uses a ramdisk as a filesystem. The
required initrd properties are injected in to the device tree blob (DTB) at
build time.
Kernel image packaged in fip as a BL33 image
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
A Linux kernel image can be packaged in the fip as a BL33 image and then
booted in TF-A.
For example, the firmware can be built as:
.. code:: shell
make PLAT=fvp DEBUG=1 \
ARM_LINUX_KERNEL_AS_BL33 \
BL33=<path-to-kernel-binary> \
INITRD_SIZE=0x8000000 \
all fip
The options ``INITRD_SIZE`` or ``INITRD_PATH`` triggers the insertion of initrd
properties in to the DTB. ``INITRD_BASE`` is also required but a default value
is set by the FVP platform.
The options available here are:
::
INITRD_BASE: Set the initrd base address in memory. Defaults to 0x90000000 in FVP.
INITRD_SIZE: Set the initrd size in dec or hex format. Hex format must precede with '0x'.
INITRD_PATH: Provide an initrd path for the build time to determine its exact size.
Users can provide either ``INITRD_SIZE`` or ``INITRD_PATH`` to set the initrd
size value. ``INITRD_SIZE`` takes prioty over ``INITRD_PATH``.
Now the fvp binary can be run as:
.. code:: shell
<path-to>/FVP_Base_AEMv8A-AEMv8A \
-C bp.secureflashloader.fname=<path-to>/bl1.bin \
-C bp.flashloader0.fname=<path-to>/fip.bin \
--data cluster0.cpu0="<path-to>/<initrd.bin>"@0x90000000
.. note::
Providing a higher value for an initrd size than the actual size of the file
is supported but it will trigger a non-breaking "Initramfs unpacking failed"
error by the kernel at runtime. This error can be ignored because initrd's
can be stacked one after another, when the kernel unpacks the first initrd it
looks for another in the extra space which it won't find, hence the error.
Preloaded kernel image - Normal flow
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -98,20 +145,6 @@ built like this:
INITRD_SIZE=0x8000000 \
all fip
The options ``INITRD_SIZE`` or ``INITRD_PATH`` triggers the insertion of initrd
properties in to the DTB. ``INITRD_BASE`` is also required but a default value
is set by the FVP platform.
The options available here are:
::
INITRD_BASE: Set the initrd base address in memory. Defaults to 0x90000000 in FVP.
INITRD_SIZE: Set the initrd size in dec or hex format. Hex format must precede with '0x'.
INITRD_PATH: Provide an initrd path for the build time to determine its exact size.
Users can provide either ``INITRD_SIZE`` or ``INITRD_PATH`` to set the initrd
size value. ``INITRD_SIZE`` takes prioty over ``INITRD_PATH``.
Now the FVP binary can be run with the following command:
.. code:: shell
@ -122,15 +155,8 @@ Now the FVP binary can be run with the following command:
--data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
--data cluster0.cpu0="<path-to>/<initrd.bin>"@0x90000000
.. note::
Providing a higher value for an initrd size than the actual size of the file
is supported but it will trigger a non-breaking "Initramfs unpacking failed"
error by the kernel at runtime. This error can be ignored because initrd's
can be stacked one after another, when the kernel unpacks the first initrd it
looks for another in the extra space which it won't find, hence the error.
Booting a preloaded kernel image - Reset to BL31 (Base FVP)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Preloaded kernel image - Reset to BL31
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
We can also boot a Linux kernel by jumping directly to BL31 ``RESET_TO_BL31=1``.
This requires preloading a DTB into memory. We can inject the initrd start and