AMD Staging Another Fix To Try Correcting Some Raven Ridge Systems On Linux
AMD Raven Ridge APUs have been out for more than one year now and at least under Linux can still be quite problematic depending upon the particular motherboard BIOS and other factors. Fortunately, while Raven 2 and Picasso APU support is appearing to be in better shape, the AMD open-source developers haven't forgot about these problematic Raven 1 systems.
Out today is the latest patch trying to help those with original Raven Ridge systems. This latest hopeful fix is now skipping over loading the DMCU firmware for Raven Ridge. DMCU in this context is the Display Micro-Controller Unit and is the micro-controller used for Panel Self Refresh (PSR) and similar functionality.
The AMDGPU Linux DRM driver has supported loading the DMCU firmware for a while now but the developers seem to believe that skipping over loading it on these Raven systems is better off rather than trying to load it and ignoring any errors. In particular, when loading the DMCU firmware on some systems with a "bad" system BIOS, it can still lead to users unable to boot their systems.
The patch is out there for review and will see if it ends up in the Linux stable series or gets tossed around some more before merging. In response to the patch, there has been a request already to white/black-list the functionality or at least offer the DMCU firmware loading as a module parameter. Without the ability to load the DMCU firmware, one missing feature is Automatic Backlight Management (ABM) for Raven Ridge laptops.