Arm Trusted Firmware: Optimizing boot time with Yocto

[Moises Araya]

Hi everyone,

I'm trying to optimize the boot time of tf-a with Yocto but don't find much information on the web. Currently tf-a takes about 1s from the point in which it is read from NOR to the point it loads UBoot from same NOR. I optimized the Linux kernel to take about 1.5s to boot (no ethernet) so the tf-a boot time has now an important weight in the whole boot time of the system.

There is this link which explains how to set some compiler flags while compiling tf-a without Yocto but didn't find the equivalent flags in Yocto.

$ make STM32MP1_DEBUG_ENABLE=0    \
            STM32MP1_UART_PROGRAMMER=0 \
            STM32MP1_USB=0             \
            STM32MP1_QSPI_NOR=0        \
            STM32MP1_QSPI_NAND=0       \
            STM32MP_FMC_NAND=1         \
            STM32MP_EMMC=0             \
            STM32MP_SDMMC=0            \
            …

As I'm booting from NOR, I trying setting the following in a bbappend:

TF_A_EXTRACONF_LEGACY=" STM32MP_SDMMC=0 STM32MP_EMMC=0 STM32MP_SPI_NOR=1 STM32MP_RAW_NAND=0 STM32MP_SPI_NAND=0 STM32MP_USE_STM32IMAGE=1"

But neither the size not the boot time of tf-a improved.

The only Yocto flag that proved useful was:

ST_TF_A_DEBUG_LOG_LEVEL = "0"

I would appreciate any help with this.

Bests,

Jose

[Olivier GALLIEN]

Hi @Moises Araya​ ,

I'm not Yocto expert but I guess you should have a look to the tfa-recipes in layers/meta-st/meta-st-stm32mp/recipes-bsp/trusted-firmware-a

For exemple in tf-a-stm32mp.inc in notice the section :

# Configure specific build flags
 
EXTRA_OEMAKE += "${@bb.utils.contains('TF_A_SIGN_ENABLE', '1', 'TRUSTED_BOARD_BOOT=1', '', d)}"
 
EXTRA_OEMAKE += "${@bb.utils.contains('TF_A_SIGN_ENABLE', '1', 'MBEDTLS_DIR=${TFA_MBEDTLS_DIR}', '', d)}"
 
EXTRA_OEMAKE += "${@bb.utils.contains('TF_A_ENCRYPTED_ENABLE', '1', 'DECRYPTION_SUPPORT=aes_gcm ENCRYPT_BL32=1', '', d)}"

I understand that adding compile flags for optimization in EXTRA_OEMAKE variable might works.

Hope it help

Olivier

[Moises Araya]

Hi @Community member​,

Thank you very much for your help. I tried setting different EXTRA_OEMAKE flags following 2 approaches:

1. Using the TF-A Makefile Flags as described in my commit of the repo
2. Using the flags that STM suggests

But the only 2 EXTRA_OEMAKE flags that helped reducing a bit the size of trusted tf-a are: DEBUG=0 LOG_LEVEL=0 but other than that, there is no noticeable change. The current size is 197kB and its boot time continues to be about 1s.

My question at this point is:

Is 1s a realistic optimized boot time for tf-a after setting the flags correctly (optimally) or I am still missing something here?

Thanks again!

Bests,

Moises