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Bug 5364

Summary: Raspberry pi 4 won't recognize the second display (kmsdrm video driver)
Product: SDL Reporter: svenvd.github
Component: *don't know*Assignee: Ryan C. Gordon <icculus>
Status: WAITING --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: danintheshed
Version: 2.0.12   
Hardware: ARM   
OS: Linux   

Description svenvd.github 2020-11-24 13:13:44 UTC 
Hi,

SDL (SDL_GetNumVideoDisplays) does not recognize the second display on a raspberry pi 4 when running with no X11(kmsdrm video driver). Higher level libraries,like pygame thus can not assign a display for particular output.

More information can be found here.

https://github.com/pygame/pygame/issues/2356

Thanks
Comment 1 Dan Lawrence 2020-11-24 13:31:49 UTC 
You can see that the kmsdrm driver is just assuming a single display here, in multiple lines like this one:

    dispdata = (SDL_DisplayData *)SDL_GetDisplayDriverData(0); //viddata->devindex);

meanwhile other video drivers that do have multi_display support do things like:

    SDL_DisplayData *pData =(SDL_DisplayData*)SDL_GetDisplayDriverData(displayIndex);


Looking back on this thread when the driver was first created:

https://discourse.libsdl.org/t/kms-drm-context-for-the-gl-gles-renderer/21813/11

it seems it was discussed and multiple displays being 'out of scope' was mentioned.
Comment 2 Sam Lantinga 2020-11-24 15:37:16 UTC 
Multiple displays are no longer out of scope. I don't have a test setup for this, does anyone have a patch they'd like considered for inclusion that supports this?