Arm is an active contributor to the EDKII project hosted by the Tianocore community.
The EDKII project is an open source project that provides a modern, feature-rich, cross-platform firmware development environment for the UEFI and PI specifications developed and maintained by the UEFI Forum.
Arm contributions make sure the EDKII project constantly keeps an up to date implementation of a UEFI compliant firmware on Arm systems.
Arm contributes to both the EDKII main repository, maintaining some core packages like DynamicTablesPkg and StandaloneMMPkg, and the EDKII platforms repository, hosting support for various Arm reference platforms as well as other 3rd party Arm-based platforms maintained by either Linaro or partners.
Arm works very closely with the Linaro EDKII maintainers and project's Stewards and it's part of the Linaro Server Firmware SIG, a Special Interest Group focusing on UEFI firmware, as well as BMC and CCIX.
Arm strives to make sure partners could easily build their UEFI drivers as AArch64 native drivers as required by the latest SBBRv1.1 specification.
Check out useful how-to guides for UEFI on Arm.