Pinephone might need larger cma size for some things

[Thra11]

Tried running sway wayland compositor. Sway runs ok. However, when I tried to launch some applications, I get:

DRM_IOCTL_MODE_CREATE_DUMB failed: Cannot allocate memory

Same problem for several applications (I think all the ones I tried were Qt quick applications).
I tried adding "cma=256M" to boot.kernelParams, rebuilt and reflashed the boot partition. Now the applications work fine.
Don't know for sure if it's a sway-specific issue: I suspect it might affect all wayland compositors. X (and applications running under X) seem to be ok with the default "cma=32M".
Not sure if limited to pinephone.

[samueldr]

It is likely not limited to the Pinephone.

It seems cma issues are chasing me these days! See NixOS/nixpkgs#97883, where the cma=32M from NixOS causes issues with the Raspberry Pi 4B!

The solution here will be:

First, to remove cma= from the command line. That's for the user.

Then, either configure a default at the kernel level, since we build bespoke kernels per-device we're free to do that. Or configure it through the device tree.

Either options are fine, and have less precedence than the command line option.

Finally, AFAIK from recent discussions and learnings, it's fine to have such a big CMA value as apparently the kernel can use the CMA to allocate anything, so it's not lost memory.

[tomfitzhenry]

Setting boot.kernelParams = "cma=128M" stopped Megapixels from crashing when the back camera took a photo. This is documented at https://nixos.wiki/wiki/PinePhone#Camera.