DMA & Cache Coherency

When to use

• Allocating DMA buffers (dma_alloc_coherent, dma_pool).
• Mapping/unmapping buffers for streaming DMA (dma_map_single, dma_map_sg, dma_unmap_*, dma_sync_single_for_cpu/device).
• Choosing between coherent and streaming mappings for a driver.
• Debugging stale/tearing data after a DMA transfer (cache lines not flushed or invalidated).
• Drivers that DMA from/to network, storage, audio, or camera devices.
• Reasoning about bounce buffers and IOMMU interaction.

When not to use