177 lines
3.9 KiB
Markdown
177 lines
3.9 KiB
Markdown
# Flattened uImage Tree documentation
|
|
|
|
[uImage.FIT] is the new format used for uImage payloads developed by
|
|
[U-boot].
|
|
|
|
## Supported architectures
|
|
|
|
* aarch64
|
|
* riscv
|
|
|
|
## Supported FIT sections
|
|
|
|
The FIT can contain multiple sections, each holding a unique
|
|
kernel, initrd or config. Out of the sections one kernel and
|
|
one initrd is chosen, depending on the matching config.
|
|
|
|
The config is selected depending on the compat string.
|
|
|
|
The section must be named in order to be found by the FIT parser:
|
|
|
|
* kernel
|
|
* fdt
|
|
* ramdisk
|
|
|
|
## Architecture specifics
|
|
|
|
The FIT parser needs architecure support.
|
|
|
|
### aarch64
|
|
The source code can be found in `src/arch/arm64/fit_payload.c`.
|
|
|
|
On aarch64 the kernel (a section named 'kernel') must be in **Image**
|
|
format and it needs a devicetree (a section named 'fdt') to boot.
|
|
The kernel will be placed close to "*DRAMSTART*".
|
|
|
|
### RISC-V
|
|
The source code can be found in `src/arch/riscv/fit_payload.c`.
|
|
|
|
On RISC-V the kernel (a section named 'kernel') must be in **Image**
|
|
format and it needs a devicetree (a section named 'fdt') to boot.
|
|
The kernel will be placed close to "*DRAMSTART*".
|
|
|
|
### Other
|
|
Other architectures aren't supported.
|
|
|
|
## Supported compression
|
|
|
|
The FIT image has to be included uncompressed into the CBFS. The sections
|
|
inside the FIT image can use different compression schemes.
|
|
|
|
Supported compression algorithms:
|
|
* LZMA
|
|
* LZ4
|
|
* none
|
|
|
|
## Compat string
|
|
|
|
The config entries contain a compatible string, that is used to find a
|
|
matching config.
|
|
|
|
The following mainboard specific functions provide the BOARDID and SKUID:
|
|
|
|
```c
|
|
uint32_t board_id(void);
|
|
```
|
|
|
|
```c
|
|
uint32_t sku_id(void);
|
|
```
|
|
|
|
By default the following compat strings are added:
|
|
|
|
* *CONFIG_MAINBOARD_VENDOR*,*CONFIG_MAINBOARD_PART_NUMBER*
|
|
* *CONFIG_MAINBOARD_VENDOR*,*CONFIG_MAINBOARD_PART_NUMBER*-rev*BOARDID*
|
|
* *CONFIG_MAINBOARD_VENDOR*,*CONFIG_MAINBOARD_PART_NUMBER*-rev*BOARDID*-sku*SKUID*
|
|
|
|
Example:
|
|
|
|
```
|
|
cavium,cn8100_sff_evb
|
|
```
|
|
|
|
If *board_id()* or *sku_id()* return invalid, the single comapt string isn't added.
|
|
|
|
You can add custom compat strings by calling:
|
|
|
|
```c
|
|
fit_add_compat_string(const char *str);
|
|
```
|
|
|
|
If no matching compat string is found, the default config is chosen.
|
|
|
|
## Building FIT image
|
|
|
|
The FIT image has to be built by calling `mkimage`. You can use
|
|
the following example configuration:
|
|
|
|
```
|
|
/*
|
|
* Simple U-Boot uImage source file containing a single kernel and FDT blob
|
|
*/
|
|
|
|
/dts-v1/;
|
|
|
|
/ {
|
|
description = "Simple image with single Linux kernel and FDT blob";
|
|
#address-cells = <1>;
|
|
|
|
images {
|
|
kernel {
|
|
description = "Vanilla Linux kernel";
|
|
data = /incbin/("Image.lzma");
|
|
type = "kernel";
|
|
arch = "arm64";
|
|
os = "linux";
|
|
compression = "lzma";
|
|
load = <0x80000>;
|
|
entry = <0x80000>;
|
|
hash-1 {
|
|
algo = "crc32";
|
|
};
|
|
};
|
|
fdt-1 {
|
|
description = "Flattened Device Tree blob";
|
|
data = /incbin/("target.dtb");
|
|
type = "flat_dt";
|
|
arch = "arm64";
|
|
compression = "none";
|
|
hash-1 {
|
|
algo = "crc32";
|
|
};
|
|
};
|
|
ramdisk-1 {
|
|
description = "Compressed Initramfs";
|
|
data = /incbin/("initramfs.cpio.xz");
|
|
type = "ramdisk";
|
|
arch = "arm64";
|
|
os = "linux";
|
|
compression = "none";
|
|
load = <00000000>;
|
|
entry = <00000000>;
|
|
hash-1 {
|
|
algo = "sha1";
|
|
};
|
|
};
|
|
};
|
|
|
|
configurations {
|
|
default = "conf-1";
|
|
conf-1 {
|
|
description = "Boot Linux kernel with FDT blob";
|
|
kernel = "kernel";
|
|
fdt = "fdt-1";
|
|
ramdisk = "ramdisk-1";
|
|
};
|
|
};
|
|
};
|
|
```
|
|
|
|
Save it as ITS file `config.its` along with the other files defined here:
|
|
* target.dtb
|
|
* initramfs.cpio.xz
|
|
* Image.lzma
|
|
|
|
Generate the `uImage` that will be included into the CBFS by calling
|
|
|
|
```bash
|
|
mkimage -f config.its uImage
|
|
```
|
|
|
|
The generated file includes a compressed initrd **initramfs.cpio.xz**, which
|
|
will be decompressed by the Linux kernel, a compressed kernel **Image.lzma**,
|
|
which will be decompressed by the FIT loader and an uncompressed devicetree blob.
|
|
|
|
[uImage.FIT]: https://raw.githubusercontent.com/u-boot/u-boot/master/doc/uImage.FIT/howto.txt
|
|
[U-Boot]: https://www.denx.de/wiki/U-Boot
|