SUSE Develops New Driver That Exposes DRM Atop FBDEV Frame-Buffer Drivers
Written by Michael Larabel in Linux Kernel on 26 March 2019 at 06:09 AM EDT. 2 Comments
SUSE developer Thomas Zimmermann has posted his work on "FBDEVDRM" as a new Direct Rendering Manager driver for exposing the DRM interfaces on top of legacy "FBDEV" frame-buffer drivers. For old frame-buffer drivers not ported to modern DRM/KMS interfaces, this could open up some interesting possibilities and at least allow these vintage display drivers to work with the likes of Plymouth and other programs only supporting the DRM interfaces.

The FBDEVDRM driver will expose the Direct Rendering Manager interfaces on top of any FBDEV hardware driver (though not the likes of VESAFB) and also uses TTM for memory management. Thomas noted with the patches, "The fbdevdrm driver runs DRM on top of fbdev framebuffer drivers. It allows for using legacy drivers with modern userspace and gives a template for converting fbdev drivers to DRM...It's not intended to add new features or drivers to fbdev. Instead fbdevdrm is supposed to be a template for converting fbdev drivers to DRM. It contains a number of comments (labeled 'DRM porting note') that explain the required steps. The license is fairly liberal to allow for combination with existing fbdev code."

This helps with programs targeting DRM interfaces like the Plymouth boot splash screen, Wayland/Weston, and others. For user-spaces supporting both FBDEV and DRM, it could allow them to be re-tooled eventually to only focus on the modern DRM APIs. While there has been calls to deprecate FBDEV, this frame-buffer device subsystem still remains within the Linux kernel but at least hardware vendors (namely embedded vendors) within recent years have finally begun focusing on providing DRM drivers rather than FBDEV. In terms of going the other way, DRM has long offered FBDEV emulation support (and these patches do account for that in ensuring FBDEVDRM doesn't latch onto an emulated FBDEV device that in turn is backed by a real DRM driver).

This SUSE-led effort will help the likes of anyone on outdated graphics hardware from Matrox, S3, Savage, SiS, Trident, and others where only FBDEV driver support is available.

We'll see where FBDEVDRM leads following today's "request for comments" and see if it makes it into the mainline Linux kernel in the near future.
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