I have found some issue regarding the drm driver for radeon with kernel in sid/stretch (I am working right now and I don't recall the correct kernel version). So I suppose there is some misunderstanding between the xorg radeon driver and drm kernel radeon driver.
Anyway this issue is only for running xorg without any /etc/X11/xorg.conf. If there is such file, the only issue is it NEEDS the BusID for card, because it fails not founding any.
Otherwise it works for 2D acceleration.
In my architecture (BIG ENDIAN PowerPC G5) there is another issue after 30 minutes, it simply hangs like some DMA-CPU or whatever and IT IS NOT RELATED TO THE BUS OR CARD ITSELF.
If I switch to use the fbdev over the radeon driver, it works fine forever.... Maybe something related to MSI Interrupt in this particular configuration???
I have to check.
For NVIDIA Driver too: I have found there are some issue on loading FCODE / BIOS Firmware Code for NV6600 (NV43). The Linux PPC64 Kernel has 64K PAGESIZE and the nvidia driver needs 4K PAGESIZE
Another issue is the firmware downloading is known to be ok in linux kernel 4.3.0-rc6.
Another issue is MESA: maybe the 11.3 version of MESA fix the BIG ENDIANNESS issue for using accelerated 3d HW on those models...
Anyone is able to confirm this?
Best regards,