eeda3d7497
Remove the incorrect usage of double underscores for the CONFIG_OF_LIST and CONFIG_SPL_OF_LIST symbols. Signed-off-by: Fabio Estevam <festevam@gmail.com>
66 lines
3.7 KiB
Plaintext
66 lines
3.7 KiB
Plaintext
MULTI DTB FIT and SPL_MULTI_DTB_FIT
|
|
|
|
The purpose of this feature is to enable U-Boot or the SPL to select its DTB
|
|
from a FIT appended at the end of the binary.
|
|
It comes in two flavors: U-Boot (CONFIG_MULTI_DTB_FIT) and SPL
|
|
(CONFIG_SPL_MULTI_DTB_FIT).
|
|
|
|
U-Boot flavor:
|
|
Usually the DTB is selected by the SPL and passed down to U-Boot. But some
|
|
platforms don't use the SPL. In this case MULTI_DTB_FIT can used to provide
|
|
U-Boot with a choice of DTBs.
|
|
The relevant DTBs are packed into a FIT (list provided by CONFIG_OF_LIST). The
|
|
FIT is automatically generated at the end of the compilation and appended to
|
|
u-boot.bin so that U-Boot can locate it and select the correct DTB from inside
|
|
the FIT.
|
|
The selection is done using board_fit_config_name_match() (same as what the SPL
|
|
uses to select the DTB for U-Boot). The selection happens during fdtdec_setup()
|
|
which is called during before relocation by board_init_f().
|
|
|
|
SPL flavor:
|
|
the SPL uses only a small subset of the DTB and it usually depends more
|
|
on the SOC than on the board. So it's usually fine to include a DTB in the
|
|
SPL that doesn't exactly match the board. There are howerver some cases
|
|
where it's not possible. In the later case, in order to support multiple
|
|
boards (or board revisions) with the same SPL binary, SPL_MULTI_DTB_FIT
|
|
can be used.
|
|
The relevant DTBs are packed into a FIT. This FIT is automatically generated
|
|
at the end of the compilation, compressed and appended to u-boot-spl.bin, so
|
|
that SPL can locate it and select the correct DTB from inside the FIT.
|
|
CONFIG_SPL_OF_LIST is used to list the relevant DTBs.
|
|
The compression stage is optional but reduces the impact on the size of the
|
|
SPL. LZO and GZIP compressions are supported. By default, the area where the
|
|
FIT is uncompressed is dynamicaly allocated but this behaviour can be changed
|
|
for platforms that don't provide a HEAP big enough to contain the uncompressed
|
|
FIT.
|
|
The SPL uses board_fit_config_name_match() to find the correct DTB within the
|
|
FIT (same as what the SPL uses to select the DTB for U-Boot).
|
|
Uncompression and selection stages happen in fdtdec_setup() which is called
|
|
during the early initialization stage of the SPL (spl_early_init() or
|
|
spl_init())
|
|
|
|
Impacts and performances (SPL flavor):
|
|
The impact of this option is relatively small. Here are some numbers measured
|
|
for a TI DRA72 platform:
|
|
|
|
+----------+------------+-----------+------------+
|
|
| size | size delta | SPL boot | boot time |
|
|
| (bytes) | (bytes) | time (s) | delta (s) |
|
|
+---------------------------+----------+------------+-----------+------------+
|
|
| 1 DTB | | | | |
|
|
+---------------------------+----------+------------+-----------+------------+
|
|
| reference | 125305 | 0 | 1.389 | 0 |
|
|
| LZO (dynamic allocation) | 125391 | 86 | 1.381 | -0.008 |
|
|
+---------------------------+----------+------------+-----------+------------+
|
|
| 4 DTBs (DRA7, DRA71, | | | | |
|
|
| DRA72, DRA72 revC) | | | | |
|
|
+---------------------------+----------+------------+-----------+------------+
|
|
| LZO (dynamic allocation) | 125991 | 686 | 1.39 | 0.001 |
|
|
| LZO (user defined area) | 125927 | 622 | 1.403 | 0.014 |
|
|
| GZIP (user defined area) | 133880 | 8575 | 1.421 | 0.032 |
|
|
| No compression (in place) | 137472 | 12167 | 1.412 | 0.023 |
|
|
+---------------------------+----------+------------+-----------+------------+
|
|
|
|
Note: SPL boot time is the time elapsed between the 'reset' command is entered
|
|
and the time when the first U-Boot (not SPL) version string is displayed.
|