https://bugs.freedesktop.org/show_bug.cgi?id=95017
--- Comment #8 from Mathieu Malaterre mathieu.malaterre@gmail.com --- (In reply to Ilia Mirkin from comment #7)
FWIW on nouveau we just default agpmode=0 in a #ifdef __powerpc__. Perhaps the same thing can work for radeon.
Well radeon_agpmode is already set to 0 already[*]. My patch force to PCI(-1) when user did not specify any value.
[*]https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/radeon/radeon_...