On Tuesday 15 January 2013, Marek Szyprowski wrote: > I'm sorry, but from my perspective this patch and the yet another dma > attribute shows that there is something fishy happening in the exynos-drm > driver. Creating a mapping in DMA address space is the MAIN purpose of > the DMA mapping subsystem, so adding an attribute which skips this > operation already should give you a sign of warning that something is > not used right. > > It looks that dma-mapping in the current state is simply not adequate > for this driver. I noticed that DRM drivers are already known for > implementing a lots of common code for their own with slightly changed > behavior, like custom page manager/allocator. It looks that exynos-drm > driver grew to the point where it also needs such features. It already > contains custom code for CPU cache handling, IOMMU and contiguous > memory special cases management. I would advise to drop DMA-mapping > API completely, avoid adding yet another dozen of DMA attributes useful > only for one driver and implement your own memory manager with direct > usage of IOMMU API, alloc_pages() and dma_alloc_pages_from_contiguous(). > This way DMA mapping subsystem can be kept simple, robust and easy to > understand without confusing or conflicting parts. Makes sense. DRM drivers and KVM are the two cases where you typically want to use the iommu API rather than the dma-mapping API, because you need protection between multiple concurrent user contexts. Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>