On Tue, Dec 08, 2020 at 01:54:00PM +0900, Tomasz Figa wrote: > >From the media perspective, it would be good to have the vmap > optional, similarly to the DMA_ATTR_NO_KERNEL_MAPPING attribute for > coherent allocations. Actually, in the media drivers, the need to have > a kernel mapping of the DMA buffers corresponds to a minority of the > drivers. Most of them only need to map them to the userspace. > > Nevertheless, that minority actually happens to be quite widely used, > e.g. the uvcvideo driver, so we can't go to the other extreme and just > drop the vmap at all. My main problem is that the DMA_ATTR_NO_KERNEL_MAPPING makes a mess of an API. I'd much rather have low-level API that returns the discontiguous allocations and another one that vmaps them rather than starting to overload arguments like in dma_alloc_attrs with DMA_ATTR_NO_KERNEL_MAPPING. > > In any case, Sergey is going to share a preliminary patch on how the > current API would be used in the V4L2 videobuf2 framework. That should > give us more input on how such a helper could look. Awesome!
