OK, that didn't work but some increasing enlightenment.
The Buildroot mechanism encourages you to take the default (typically minimal) kernel config from the board definition and then add any extras you need via a kernel config fragment file. However, that doesn't really work well with raspberrypi4_64_defconfig because that uses the default bcm2711 kernel config - while the resulting kernel is somewhat minimal, all sorts of things are turned on as modules. The kicker here is that you can't enable a module as built-in if any of its dependencies are enabled as modules, and if you try from a fragment file then instead of an error or the dependencies being turned to built-in, your added item gets silently turned back into a module. The modules probably get built but don't end up on the final filesystem image. It ought to be possible to get what you want by overriding everything needed, as I tried with the list I posted earlier, but I must have missed one - and in any case when you've gone that far there's not really much point in the default + overrides approach, might as well go for a complete kernel config in the project files (and keep a README of what went into it), as neither the overrides nor the complete config are likely to be future-proof.
Anyhow, back to debugging the manually-configured system.
This now probes VC4, and /dev/dri has appeared. With the first attempt, the application coredumped in the SDL/fbdev initialisation.
With a kernel configured with 200% buffer allocation for fbdev (which the kernel config help suggests for double buffering), the app now runs but produces no display - so it seems like SDL is still talking to the simple fbdev driver used at boot which has had the hardware pulled from under it by VC4. 'fbset' still reports accel=false and the different pixel format options compared to the full-OS build.
So it looks like I'm still missing some piece of the VC4 architecture that allows it to be used. I haven't got any of the video codecs (which are probed on the full-OS) - do I need the full set of everything?
The Buildroot mechanism encourages you to take the default (typically minimal) kernel config from the board definition and then add any extras you need via a kernel config fragment file. However, that doesn't really work well with raspberrypi4_64_defconfig because that uses the default bcm2711 kernel config - while the resulting kernel is somewhat minimal, all sorts of things are turned on as modules. The kicker here is that you can't enable a module as built-in if any of its dependencies are enabled as modules, and if you try from a fragment file then instead of an error or the dependencies being turned to built-in, your added item gets silently turned back into a module. The modules probably get built but don't end up on the final filesystem image. It ought to be possible to get what you want by overriding everything needed, as I tried with the list I posted earlier, but I must have missed one - and in any case when you've gone that far there's not really much point in the default + overrides approach, might as well go for a complete kernel config in the project files (and keep a README of what went into it), as neither the overrides nor the complete config are likely to be future-proof.
Anyhow, back to debugging the manually-configured system.
This now probes VC4, and /dev/dri has appeared. With the first attempt, the application coredumped in the SDL/fbdev initialisation.
With a kernel configured with 200% buffer allocation for fbdev (which the kernel config help suggests for double buffering), the app now runs but produces no display - so it seems like SDL is still talking to the simple fbdev driver used at boot which has had the hardware pulled from under it by VC4. 'fbset' still reports accel=false and the different pixel format options compared to the full-OS build.
So it looks like I'm still missing some piece of the VC4 architecture that allows it to be used. I haven't got any of the video codecs (which are probed on the full-OS) - do I need the full set of everything?
Statistics: Posted by arg001 — Tue Oct 08, 2024 8:58 am