Introduction

Hello and Welcome to the blog on “Avenger96 Mainlining Update - Part 1”. This blog will summarise the recent mainlining efforts for Avenger96 board in Linux kernel, U-Boot, Trusted Firmware and Zephyr RTOS.

Avenger96 Board

Avenger96 board is one of the 96Boards Consumer Edition of the 96Boards platform. Avenger96 board is based on STM32MP1 heterogeneous SoC (dual Arm Cortex-A7 cores and an Arm Cortex-M4 core) from STMicroelectronics. In addition, an extensive set of interfaces and connectivity peripherals are included to interface to cameras, touch-screen displays an MMC/SD cards. It also fully supports wireless communication, including WLAN, Ethernet and BLE.

Following are the features of the board:

SoC: STM32MP157AAC PMIC: STPMIC1A RAM: 1024 Mbyte @ 533MHz Storage: eMMC v4.51: 8 Gbyte microSD Socket: UHS-1 v3.01 Ethernet Port: 10/100/1000 Mbit/s, IEEE 802.3 Compliant Wireless: WiFi 5 GHz & 2.4GHz IEEE 802.11a/b/g/n/ac Bluetooth ® wireless technology v4.2 (BR/EDR/BLE) USB: 2x Type A (USB 2.0) Host and 1x Micro B (USB 2.0) OTG Display: HDMI: WXGA (1366x768)@ 60 fps, HDMI 1.4 LED: 4x User LED, 1x WiFi LED, 1x BT LED

Mainlining Update

STMicroelectronics did a great job in upstreaming the SoC and eval boards support to various open source projects such as Linux kernel, U-Boot, ARM Trusted Firmware-A, Zephyr, etc… So it became very easy for me to upstream the Avenger96 board to all open source projects mentioned above. This is the kind of base support we expect from our partners and STMicroelectronics really stood out and lead from the front.

Linux Kernel

Linux kernel upstreaming started with adapting the existing STM32MP157A-DK1 evaluation board. I had to add few missing pinmux definitions for this board and rest of the stuffs were mostly same. At that time, only basic features were supported in mainline for STM32MP1, so just enabled the ones which were supported and submitted the patchset to LKML.

During the initial review, Rob Herring (Devicetree/bindings Maintainer) spotted some corrections in the way STM32MP1 SoC bindings are laid out. So, I went ahead and converted the old platform binding (.txt) to the newly introduced JSON schema format. The JSON schema format really helps in validating the devicetree before getting processed by the devicetee compiler, so conversion seemed obvious to me.

And at the 4th iteration of the patchset, the STM32MP1 platform maintainer merged the series to his stm32-next branch for v5.3.

Link to final patchset: https://lkml.org/lkml/2019/6/12/161

U-Boot

As like Linux kernel, U-Boot board support was also pretty easy since the SoC was already well supported. I just added the missing pinmux definitions and rest of the stuffs were mostly same with STM32MP157A-DK1 board. During the testing, I faced some issues with board not booting when SPL way of booting was used. After debugging, it turned out that I had to add u-boot,dm-pre-alloc property to some devicetree nodes in order to make it available in SPL.

Finally, I submitted the patchset and at 2nd iteration, it was merged by the platform maintainer.

Link to final patchset: https://www.mail-archive.com/u-boot@lists.denx.de/msg324986.html

ARM Trusted Firmware-A

Trusted firmware support was necessary to boot the board since it provides the second stage bootloader which loads u-boot. Hence, I also added support for Avenger96 board by following the existing STM32MP157A-DK1 board.

As like Linux kernel and u-boot, only pinmux changes were required along with some board specific bits. So after finishing those, I quickly submitted the board support as a gerrit review and it got merged smoothly.

Link to gerrit review: https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/960

Zephyr RTOS

After finishing all the board support needed to run Linux kernel on Cortex A7 cores, there was one remaining but interesting work left! It was the firmware to run on Cortex-M4 core. Since STMicroelectronics has been contributing heavily to the Zephyr RTOS project, they decided to run Zephyr RTOS on M4 core to offload the real time tasks. And as like other projects, they also added basic SoC and evaluation board support in Zephyr. So, I just adapted the existing board support to Avenger96 and boom!!!, Zephyr RTOS was running on M4 core along with Linux kernel on A7 cores.

At that time, the Zephyr support was very basic such that there was no proper IPC mechanisms were available to communicate to the Linux kernel over mailbox. But, ST folks already started working on OpenAMP library support and very soon we should see both Linux and Zephyr talking to each other :-)

Link to PR: https://github.com/zephyrproject-rtos/zephyr/pull/16784

Note: For loading the Zephyr binary to M4 core, I used u-boot.

Conclusion

So this ends the quick summary of the upstreaming efforts for Avenger96 board from Arrow Electronics. Lots of features are being added to the above mentioned open source projects, so we will keep an eye on it and enable the relevant features on Avenger96 when available. Stay tuned for Part-2 blog!

This article is Part 1 in a 1-Part Series.