Building WPE for an embedded device

WPE Stack

WebKit Process Model (1/2)

WebKit Process Model (2/2)

libwpe interfaces

WPE backends: libwpe implementations

• Used by the WPE port
• Provides the implementation of the interfaces defined by the libwpe for rendering and input handling
• Sets EGL resources as requirement for the graphical output consuption (OpenGLv2)
• Several implementations but the most relevant are: wpebackend-rdk, wpebackend-fdo, …

WPEBackend-rdk

• RDK is a Set-top boxes consortium
• Covers different STB hardware and proptotype boards
• Uses a propietary API (Dispmanx) to lowest level access to the GPU
• It is supported by the propietary RPi Broadcom driver

WPEBackend-fdo

• Uses Wayland protocol to coordinate the operations among the interface implementations
• Depends on the Wayland EGL support (EGL_WL_bin_wayland_display)
• Relies in GLib as IPC mechanism for comunication in between the host and the backend
• In theory, compatible with any Mesa driver implementation

• Conclusion 1: Several libs combinations (libwpe, libwebkit, cog …) and several backend implementations that makes a bit difficult the setup.

• Conclusion 2: WPE configuration is sensitive to the underlying hardware and software stack where it has to work

What makes a hardware platform

• System-on-Chip (SoC)
• GPU
• CPU

Example (1/3): NXP i.MX 6

• SoC: i.MX6Q
• GPU: Vivante GC2000 / GC320
• CPU: NXP i.MX 6 - Cortex-A9 - quad-core

Example (2/3): Raspberri Pi 4 B

• SoC: BCM2711B0
• GPU: Broadcom VideoCore VI 500MHz
• CPU: A72 - quad-core

Example (3/3): Qualcomm

• SoC: APQ8017
• GPU: Adreno 306
• CPU: Qualcomm - Cortex-A53 CPU

… More supported hardware

wpewebkit.org/about/supported-hardware

• Conclusion 3: WPE works in the top of several multiple different hardware platforms

Board Support Package (BSP)

• Problem 1: Several libs and dependencies that makes a bit difficult the the setup.

• Problem 2: WPE is sensitive to the underlying hardware and software stack where it has to work

• Problem 3: WPE works in the top of several multiple different hardware platforms

• Solution: A software layer that enables an hardware-specific platform: BSP

Board Support Package (1/3)

• Bootloader and Linux kernel
• SoC operative system support:
  • SoC support (peripherals, storage, network, …)
  • Graphics stack support
• Userspace tools and interfaces
• WebKit stack:
  • libwpe
  • WPE backend implementation
  • WebKit WPE runtime
  • WPE browser (cog)

Board Support Package (2/3)

Board Support Package (3/3)

• Assembling all the user space components needed for the system, configure them, develop the upgrade and recovery mechanisms, etc.
• Application development: write the company-specific applications and libraries.
• Building from source
• Cross-compilation
• Recipes for building components

Yocto (1/2)

• YP is not a distro but is something that allow you to build your own distro …
• Combines, maintains and validates three key development elements: …

Yocto (2/2)

1. A set of integrated tools to make working with embedded Linux successful, including tools for automated building and testing: Bitbake, Wic …
2. Poky: A reference embedded distribution
3. The OpenEmbedded build system, co-maintained with the OpenEmbedded Project

The Yocto build enviroment is structurated in layers. Let’s see the layers like a set of recipes, classes and definitions that extend the base distribution.

meta-webkit

• Created on Oct 2015 by Carlos López (blog).

• meta-webkit is an compatible Yocto BSP meta-layer which provides recipes for WebKitGTK and WPE:

  • The runtime and libraries for wpe and webkitgtk
  • The libwpe
  • The WPE backends implementations: wpebackend-fdo and wpebackend-rdk
  • and the reference WPE browser: cog

meta-webkit:

├── conf
│   └── layer.conf
├── recipes-browser
│   ├── cog
│   │   └── cog_0.8.0.bb
│   ├── libwpe
│   │   └── libwpe_1.8.0.bb
│   ├── webkitgtk
│   │   └── webkitgtk_2.32.0.bb
│   ├── wpebackend-fdo
│   │   └── wpebackend-fdo_1.8.3.bb
│   └── wpewebkit
│       └── wpewebkit_2.32.0.bb
└── ...

WPE on a RPi (meta-webkit)

1. Specify architecture, policies, patches …
2. Fetches and downloads the source code
3. Extracts the sources into a local work area
4. Build binary packages
5. QA and sanity checks
6. Build system generates root file image
7. Build system generates the system image and the extensible SDK (eSDK)

Getting the sources and activate the environment

cd ${HOME}/yocto-rpi3-wpe
git clone https://git.yoctoproject.org/git/poky -b hardknott
git clone git://git.openembedded.org/meta-openembedded -b hardknott
git clone https://github.com/OSSystems/meta-gstreamer1.0 -b master
git clone https://git.yoctoproject.org/git/meta-raspberrypi -b master
git clone https://github.com/Igalia/meta-webkit -b master

$ source poky/oe-init-build-env

bblayers.conf:

$ cat conf/bblayers.conf

BSPDIR := "${@os.path.abspath(os.path.dirname(d.getVar('FILE', True)) + '/../..')}"

BBLAYERS = " ${BSPDIR}/poky/meta \
  ${BSPDIR}/poky/meta-poky \
  ${BSPDIR}/poky/meta-yocto-bsp \
  ${BSPDIR}/meta-openembedded/meta-oe \
  ${BSPDIR}/meta-openembedded/meta-python \
  ${BSPDIR}/meta-gstreamer1.0 \
  ${BSPDIR}/meta-raspberrypi \
  ${BSPDIR}/meta-webkit \
"

local.conf:

$ cat local.conf
MACHINE = 'raspberrypi3'
MACHINE_FEATURES_append = " vc4graphics"
GPU_MEM_256 = "128"
GPU_MEM_512 = "196"
GPU_MEM_1024 = "396"
EXTRA_IMAGE_FEATURES = "debug-tweaks"
IMAGE_FEATURES_append = " ssh-server-dropbear hwcodecs"
DISABLE_VC4GRAPHICS = "1"
PREFERRED_PROVIDER_virtual/wpebackend = "wpebackend-fdo"
PREFERRED_PROVIDER_virtual/libwpe = "libwpe"
IMAGE_INSTALL_append = " cog wpewebkit"

Run bitbake

$ bitbake core-image-weston
Loading cache: 100% |#################| Time: 0:00:00
Loaded 3376 entries from dependency cache.
Parsing recipes: 100% |#################| Time: 0:20:00
Build Configuration:
BB_VERSION         = "1.36.0"
BUILD_SYS          = "x86_64-linux"
NATIVELSBSTRING    = "universal"
TARGET_SYS         = "arm-linux-gnueabi"
MACHINE            = "raspberrypi3"
DISTRO             = "poky"
DISTRO_VERSION     = "1.0.0"
meta
meta-poky
meta-yocto-bsp     = "hardknott"
meta-oe
...

$ ls tmp/deploy/images/raspberrypi3/*wic
tmp/deploy/images/raspberrypi3/core-image-weston.wic

Running Cog in RPi

root@raspberrypi3:~# export WAYLAND_DISPLAY=wayland-0
root@raspberrypi3:~# export XDG_RUNTIME_DIR=/run/user/0
root@raspberrypi3:~# cog -P fdo http://wpewebkit.org