Modified vc4 Linux kernel module

This contains the downstream RaspberrryPi Linux kernel version with the following modifications/patches:

1. A patch to enable interlaced video modes for the DPI port (see raspberrypi/linux#2668). Picked up from the Recalbox project, which included them in their Linux kernel patches (here for instance).

Installation

This out-of-tree kernel module is supported only for RaspiOS distributions since it uses the Debian packages specific to it.

The installation of the module is meant to be done via dkms. The build steps will download the driver files for the kernel version from Github. The commit hash of the tree from which the driver files are fetched is found from the RaspiOS linux-image package changelog file (see the included Makefile). Reboot after installation

Installation commands:

# clone the repo 
git clone https://github.com/cmitu/vc4-dkms

# tell DKMS about the module
sudo dkms add vc4-dkms

# build and install the module
sudo dkms install vc4-dkms/1.2

# reboot to activate the module
sudo reboot

Once installed, the module will be re-built on kernel updates

Update/Removal

To update to a new version of the module from this repo, remove the driver with sudo dkms remove -m vc4-dkms -v 1.2 and then repeat the installation steps above.

To find out which version(s) are installed just run dkms status and look at the output:

vc4-dkms/x.y, 6.12.47+cmitu-rpi-v8, riscv64: installed (Original modules exist)
...

In the output above the x.y part in the first column represents the version number, which should be passed as the value to the -v parameter in the removal command:

sudo dkms remove -m vc4-dkms -v x.y --all

Note on kernel and OS versions support

• The kernel versions supported are 6.1.x an up, on RaspiOS 12 ("bookworm") and up.
• The installation of a development kernel with rpi-update is not supported, and dkms wouldn't work anyway without the correspoding rpi-source invocation.
• Using an initramfs hasn't been tested and the updated module will probably not be included automatically in the initramfs generated by the stock RaspiOS kernel package.