Build

Three repositories, side by side:

• linux_mainline_rm696: the kernel. Linux 6.18.55 from linux-stable, with this port's changes as commits on branch rm696 (see The kernel).
• pvr_sgx_rm696: the SGX (GPU) driver, built as modules against the kernel; its README has the driver's origin and its changes for 6.18.
• rm696_mainline_port: the build kit. The initramfs's init (ramboot/release-init), the build script (kernel/build.sh) and these docs.

git clone https://github.com/zsavajji/rm696_mainline_port
git clone --depth 1 --branch rm696 https://github.com/zsavajji/linux_mainline_rm696
git clone https://github.com/zsavajji/pvr_sgx_rm696
cd rm696_mainline_port
RELEASE=1 kernel/build.sh

The result is build/zImage-n9-release, ready for NOLO (the zImage with the N9's device tree appended and the initramfs built in). A full build takes a few minutes on a recent machine.

What the build needs

A Linux machine, or one you can reach over SSH (below). On Debian 13 (other distributions name the packages alike):

sudo apt install gcc gcc-arm-linux-gnueabihf make bc bison flex libssl-dev libelf-dev \
  git rsync curl cpio xz-utils kmod openssh-client

The build downloads the rest:

• from Alpine Linux v3.24 (armv7): the static BusyBox and dropbear for the initramfs;
• from wireless-regdb: the signed regulatory database.

Nothing of Nokia's is needed or included: the phone loads its own firmware, the WLAN chip's included (see Firmware). Their licences, for anyone passing the image on: BusyBox is GPL-2.0 (its source is Alpine's), dropbear and musl are MIT, and wireless-regdb is ISC.

Where it builds

kernel/build.sh takes its settings from the environment:

Variable	Default	Meaning
RELEASE	(empty)	1 builds the release image. Without it the build is the project's RAM-boot test image, for development only: it keeps the phone's disks read-only and lets in the SSH key made at the first build (build/ramboot-key)
BOX	local on Linux; on macOS the project's own build VM, so set it there	local builds here, in build/box, from the kernel repository as it is checked out. Anything else is an SSH destination (user@host) that builds in its ~/projects/sgx, with the kernel's BRANCH pushed there as committed
BOX_SSH_CONFIG		an SSH config file for reaching BOX
KERNEL	../linux_mainline_rm696	the kernel repository
PVR	../pvr_sgx_rm696	the SGX driver's checkout, built as it is checked out (also over SSH)
BRANCH	rm696	the branch or tag built on a BOX over SSH
CROSS	arm-linux-gnueabihf-	the cross compiler's prefix on the machine that builds

The build leaves two cores free; the kernel and its modules go to build/box/projects/sgx/build (or the box's ~/projects/sgx/build), the image to build/.

From macOS

A kernel doesn't build on macOS, and a kernel checkout on macOS's case-insensitive disk loses files that differ only in case. Build on a Linux machine or VM over SSH: the kernel's commits are pushed there, so the Mac needs no checkout of its files.

git clone --no-checkout https://github.com/zsavajji/linux_mainline_rm696
git clone https://github.com/zsavajji/pvr_sgx_rm696
cd rm696_mainline_port
BOX=you@linux-box RELEASE=1 kernel/build.sh

The box needs the packages above, and enough room for the kernel (about 5 GB).

Changing the kernel

The kernel's configuration is omap2plus_defconfig with arch/arm/configs/rm696.config on top. kernel/build.sh checks that every line of rm696.config made it into the final configuration (a missing dependency drops an option silently) and stops if one didn't. Change the fragment or the code, commit, and build again; Removed and switched off lists what the configuration leaves out and how to put each back.

Checking the SGX driver's interface

Harmattan's GPU libraries are closed and talk to the kernel through pvrsrvkm's ioctls, so the driver must dispatch them exactly as Nokia's module did. check-abi.py compares the two modules' ioctl dispatch without a phone. It lives with the driver, in pvr_sgx_rm696 (by default it reads this kit's build/pvrsrvkm.ko); its header says how to extract Nokia's pvrsrvkm.ko from the PR1.3 firmware image. It needs llvm-objdump.