Understanding Panfrost startup

[hjalfi]

Hello,

I have an Asus Chromebook C100P with a Mali GPU.

When I boot the latest Arch Linux on it, the screen remains black during startup until about T+7, when it comes on and displays messages which scroll off the screen too fast to read. I can't find anything obvious in the systemctl logs but the dmesg logs seem to indicate that's when the panfrost driver and DRM stuff gets loaded.

What in userland is causing this to happen? And is there any way of making this happen earlier --- ideally, when the kernel itself loads? I'm losing lots of startup logging and if things go wrong before the screen is turned on I just get an undebuggable black screen.

[sehraf]

As a start, you can blacklist the panfrost module. I have a TV box that shows the same symptoms: black screen when panfrost is loaded.
The problem with panfrost is that it is still WIP. AFAIk there was an attempt to only enabled it (the module) on well tested hardware. Could be that this patch is already in 5.3.

[hjalfi]

For me it was the other way round, actually. The screen wasn't lighting up until one of the many Panfrost modules got loaded. Blacklisting it wouldn't have worked.

AFAICT what happens is that systemd normally loads the module by autodetecting the hardware and then attempting to load a particular module name based on a magic string which modules.aliases maps onto the real panfrost module; but it wasn't, because systemd.

For me the solution was to add the module to /etc/modules so that they got loaded early. I still don't know which one I actually need, ending up simply loading panfrost plus a bunch of the rockchip drm and vpu modules, but it seems to work.

It'd be really nice if these could be included with the kernel. They're always needed, or else the screen doesn't work, and debugging when things don't work is pretty hard without them...