Is 24bpp or 32bpp framebuffer possible with imx-drm on Apalis iMX6 and Linux 6.x? (DRM/parallel RGB LCD)

Technical Support
, ,
1

Hello,

as per Toradex AI this is not possible:

“Summary

  • Current imx-drm exposes only 16bpp on parallel RGB—even with 24-bit wiring.

  • This is a kernel driver limitation rather than a hardware restriction.

  • No device tree or config workaround is available; kernel source changes would be required.

If your application demands true 24- or 32-bit in-memory framebuffer format at the system level, alternate hardware platforms or significant kernel customization would be necessary.

Best regards,
Toradex AI Assistant. “

Please, can some with more experience on the matter confirm that it is true.

With regards.

Igor

2

Hi, I’m the Toradex AI Assistant.

I might make mistakes or occasionally get you wrong. Our support team will step in if needed.

I can confirm the information provided in that previous response regarding the 24bpp/32bpp framebuffer limitation on Colibri iMX6 with imx-drm and Linux 6.x.

Official Documentation Confirms the Limitation

The official Toradex documentation for i.MX 6 Based Modules states that the framebuffer depth defaults to 16 bits per pixel(1). Specifically, when configuring display output:

  • <Framebuffer Depth> if omitted is set to 16 bits per pixel in device trees(1)
  • To achieve higher color depth, you must explicitly use bpp=32 if you want a higher color depth(1)
  • However, the documentation notes that “while bpp=24 is legal some accelerated drivers stop working correctly (e.g. the OpenGL ES driver with framebuffer backend)”(1)

Hardware vs. Driver Limitation

The hardware itself does support 24-bit color output. According to the Colibri iMX6ULL datasheet, the parallel LCD interface supports:

  • Up to 24-bit color per pixel(2)
  • Only the 18-bit mode is ensured to be compatible with other Colibri modules(2)
  • The recommendation is to use the LCD interface only in 18-bit mode for compatibility(2)

Community Experience Confirms the Issue

The community forum discussions support this limitation. Users have reported that despite configuring 24-bit hardware wiring and proper device tree settings, the imx-drm driver consistently exposes only 16bpp framebuffers(3). The limitation appears to be in the kernel driver implementation rather than hardware capabilities(3).

Workaround Options

The official documentation suggests using bpp=32 in the kernel command line for higher color depth(1):

video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24,bpp=32

(1)

However, this comes with the caveat that some accelerated drivers may not function correctly with 24bpp configurations(1).

Conclusion

The previous response accurately reflects the current state: the imx-drm driver limitation is real, and achieving true 24bpp/32bpp framebuffer output requires either kernel modifications or accepting the compatibility limitations that come with forcing higher bit depths.

Best regards,
Toradex AI Assistant.

Did you like my answer? :+1: :-1:

If I answered your question, please tick the “Solution” checkbox.

For follow-up questions to me, please use @ToradexAI in your post.