STM32MP1 devices like the STM32MP157C Discovery Kit are officially supported by STMicroelectronics through the OpenSTLinux distribution, a set of OpenEmbedded layers.
The trouble starts when you'd like to create a minimum distribution based on newer software. With OpenSTLinux, the result is usually bloated and outdated. Newer Yocto releases support basically everything you want -- unfortunately, using OpenSTLinux with these is basically impossible.
The solution is to use the essential part of OpenSTLinux concerning hardware support, i.e. the BSP layer together with a reference distribution like Poky. This way, you can provide support for newer Yocto releases, you get rid of the OpenSTLinux bloat and you can rely on the Yocto documentation.
The aim of this layer is to provide missing pieces like machine definitions and WKS files which help you create flash images.
Currently, the STM32MP157C-DK2 is supported, adding support for additional devices shouldn't be hard.
URI: https://github.com/STMicroelectronics/meta-st-stm32mp
branch: zeus
If you base your distribution on Poky, your bblayers.conf could look like this:
BBLAYERS ?= " \
/opt/yocto/workspace/layers/poky/meta \
/opt/yocto/workspace/layers/poky/meta-poky \
/opt/yocto/workspace/layers/poky/meta-yocto-bsp \
/opt/yocto/workspace/layers/meta-openembedded/meta-oe \
/opt/yocto/workspace/layers/meta-openembedded/meta-python \
/opt/yocto/workspace/layers/meta-st-stm32mp \
/opt/yocto/workspace/layers/meta-rs-stm32mp \
"
Set the machine:
MACHINE = "stm32mp157c-dk2"
Set file system types in order to generate a wic file which can be written to a SD card with Etcher:
IMAGE_FSTYPES = "ext4 wic"
TODO: wic.gz would be desireable, but doesn't seem to work, it causes errors regarding missing ext4 files.
Accept the EULA to enable all features of the BSP layer (e.g. GPU):
ACCEPT_EULA_stm32mp157c-dk2 = "1"
Adjust the root partition size (in megabytes):
STM32MP_ROOTFS_FIXED_SIZE = 256