mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-04 02:20:25 +00:00
50f566d6ee
Update README.falcon to use "none" for compression property for ramdisk image to avoid being uncompressed upon loading. Signed-off-by: York Sun <york.sun@nxp.com>
150 lines
6.5 KiB
Text
150 lines
6.5 KiB
Text
Falcon boot option
|
|
------------------
|
|
Falcon boot is a short cut boot method for SD/eMMC targets. It skips loading the
|
|
RAM version U-Boot. Instead, it loads FIT image and boot directly to Linux.
|
|
CONFIG_SPL_OS_BOOT enables falcon boot. CONFIG_SPL_LOAD_FIT enables the FIT
|
|
image support (also need CONFIG_SPL_OF_LIBFDT, CONFIG_SPL_FIT and optionally
|
|
CONFIG_SPL_GZIP).
|
|
|
|
To enable falcon boot, a hook function spl_start_uboot() returns 0 to indicate
|
|
booting U-Boot is not the first choice. The kernel FIT image needs to be put
|
|
at CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR. SPL mmc driver reads the header to
|
|
determine if this is a FIT image. If true, FIT image components are parsed and
|
|
copied or decompressed (if applicable) to their destinations. If FIT image is
|
|
not found, normal U-Boot flow will follow.
|
|
|
|
An important part of falcon boot is to prepare the device tree. A normal U-Boot
|
|
does FDT fixups when booting Linux. For falcon boot, Linux boots directly from
|
|
SPL, skipping the normal U-Boot. The device tree has to be prepared in advance.
|
|
A command "spl export" should be called under the normal RAM version U-Boot.
|
|
It is equivalent to go through "bootm" step-by-step until device tree fixup is
|
|
done. The device tree in memory is the one needed for falcon boot. Falcon boot
|
|
flow suggests to save this image to SD/eMMC at the location pointed by macro
|
|
CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR, with maximum size specified by macro
|
|
CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORS. However, when FIT image is used for
|
|
Linux, the device tree stored in FIT image overwrites the memory loaded by spl
|
|
driver from these sectors. We could change this loading order to favor the
|
|
stored sectors. But when secure boot is enabled, these sectors are used for
|
|
signature header and needs to be loaded before the FIT image. So it is important
|
|
to understand the device tree in FIT image should be the one actually used, or
|
|
leave it absent to favor the stored sectors. It is easier to deploy the FIT
|
|
image with embedded static device tree to multiple boards.
|
|
|
|
Macro CONFIG_SYS_SPL_ARGS_ADDR serves two purposes. One is the pointer to load
|
|
the stored sectors to. Normally this is the static device tree. The second
|
|
purpose is the memory location of signature header for secure boot. After the
|
|
FIT image is loaded into memory, it is validated against the signature header
|
|
before individual components are extracted (and optionally decompressed) into
|
|
their final memory locations, respectively. After the validation, the header
|
|
is no longer used. The static device tree is copied into this location. So
|
|
this macro is passed as the location of device tree when booting Linux.
|
|
|
|
Steps to prepare static device tree
|
|
-----------------------------------
|
|
To prepare the static device tree for Layerscape boards, it is important to
|
|
understand the fixups in U-Boot. Memory size and location, as well as reserved
|
|
memory blocks are added/updated. Ethernet MAC addressed are updated. FMan
|
|
microcode (if used) is embedded in the device tree. Kernel command line and
|
|
initrd information are embedded. Others including CPU status, boot method,
|
|
Ethernet port status, etc. are also updated.
|
|
|
|
Following normal booting process, all variables are set, all images are loaded
|
|
before "bootm" command would be issued to boot, run command
|
|
|
|
spl export fdt <address>
|
|
|
|
where the address is the location of FIT image. U-Boot goes through the booting
|
|
process as if "bootm start", "bootm loados", "bootm ramdisk"... commands but
|
|
stops before "bootm go". There we have the fixed-up device tree in memory.
|
|
We can check the device tree header by these commands
|
|
|
|
fdt addr <fdt address>
|
|
fdt header
|
|
|
|
Where the fdt address is the device tree in memory. It is printed by U-Boot.
|
|
It is useful to know the exact size. One way to extract this static device
|
|
tree is to save it to eMMC/SD using command in U-Boot, and extract under Linux
|
|
with these commands, repectively
|
|
|
|
mmc write <address> <sector> <sectors>
|
|
dd if=/dev/mmcblk0 of=<filename> bs=512 skip=<sector> count=<sectors>
|
|
|
|
Note, U-Boot takes values as hexadecimals while Linux takes them as decimals by
|
|
default. If using NAND or other storage, the commands are slightly different.
|
|
When we have the static device tree image, we can re-make the FIT image with
|
|
it. It is important to specify the load addresses in FIT image for every
|
|
components. Otherwise U-Boot cannot load them correctly.
|
|
|
|
Generate FIT image with static device tree
|
|
------------------------------------------
|
|
Example:
|
|
|
|
/dts-v1/;
|
|
|
|
/ {
|
|
description = "Image file for the LS1043A Linux Kernel";
|
|
#address-cells = <1>;
|
|
|
|
images {
|
|
kernel {
|
|
description = "ARM64 Linux kernel";
|
|
data = /incbin/("./arch/arm64/boot/Image.gz");
|
|
type = "kernel";
|
|
arch = "arm64";
|
|
os = "linux";
|
|
compression = "gzip";
|
|
load = <0x80080000>;
|
|
entry = <0x80080000>;
|
|
};
|
|
fdt-1 {
|
|
description = "Flattened Device Tree blob";
|
|
data = /incbin/("./fsl-ls1043ardb-static.dtb");
|
|
type = "flat_dt";
|
|
arch = "arm64";
|
|
compression = "none";
|
|
load = <0x90000000>;
|
|
};
|
|
ramdisk {
|
|
description = "LS1043 Ramdisk";
|
|
data = /incbin/("./rootfs.cpio.gz");
|
|
type = "ramdisk";
|
|
arch = "arm64";
|
|
os = "linux";
|
|
compression = "none";
|
|
load = <0xa0000000>;
|
|
};
|
|
};
|
|
|
|
configurations {
|
|
default = "config-1";
|
|
config-1 {
|
|
description = "Boot Linux kernel";
|
|
kernel = "kernel";
|
|
fdt = "fdt-1";
|
|
ramdisk = "ramdisk";
|
|
loadables = "fdt", "ramdisk";
|
|
};
|
|
};
|
|
};
|
|
|
|
The "loadables" is not optional. It tells SPL which images to load into memory.
|
|
|
|
Falcon mode with QSPI boot
|
|
--------------------------
|
|
To use falcon mode with QSPI boot, SPL needs to be enabled. Similar to SD or
|
|
NAND boot, a RAM version full feature U-Boot is needed. Unlike SD or NAND boot,
|
|
SPL with QSPI doesn't need to combine SPL image with RAM version image. Two
|
|
separated images are used, u-boot-spl.pbl and u-boot.img. The former is SPL
|
|
image with RCW and PBI commands to load the SPL payload into On-Chip RAM. The
|
|
latter is RAM version U-Boot in FIT format (or legacy format if FIT is not
|
|
used).
|
|
|
|
Other things to consider
|
|
-----------------------
|
|
Falcon boot skips a lot of initialization in U-Boot. If Linux expects the
|
|
hardware to be initialized by U-Boot, the related code should be ported to SPL
|
|
build. For example, if Linux expect Ethernet PHY to be initialized in U-Boot
|
|
(which is not a common case), the PHY initialization has to be included in
|
|
falcon boot. This increases the SPL image size and should be handled carefully.
|
|
If Linux has PHY driver enabled, it still depends on the correct MDIO bus setup
|
|
in U-Boot. Normal U-Boot sets the MDC ratio to generate a proper clock signal.
|