The Xilinx DRM driver uses the GEM (Graphics Execution Manager) memory manager and implements DRM PRIME buffer sharing. PRIME is the cross-device buffer sharing framework in DRM. To user-space PRIME buffers are DMABUF-based file descriptors. The DRM GEM/CMA helpers use the Continuous Memory Access (CMA) allocator as a means to provide buffer objects that are physically contiguous in memory. This is useful for display drivers that are unable to map scattered buffers via an I/O memory management unit (IOMMU).
Frame buffers are abstract memory objects that provide a source of pixels to scan out to a CRTC. Applications explicitly request the creation of frame buffers and receive an opaque handle that can be passed to the KMS CRTC control, plane configuration, and page flip functions.