Hi Christoph, On 19.08.2020 08:55, Christoph Hellwig wrote: > this series replaced the DMA_ATTR_NON_CONSISTENT flag to dma_alloc_attrs > with a separate new dma_alloc_pages API, which is available on all > platforms. In addition to cleaning up the convoluted code path, this > ensures that other drivers that have asked for better support for > non-coherent DMA to pages with incurring bounce buffering over can finally > be properly supported. > > I'm still a little unsure about the API naming, as alloc_pages sort of > implies a struct page return value, but we return a kernel virtual > address. The other alternative would be to name the API > dma_alloc_noncoherent, but the whole non-coherent naming seems to put > people off. As a follow up I plan to move the implementation of the > DMA_ATTR_NO_KERNEL_MAPPING flag over to this framework as well, given > that is also is a fundamentally non coherent allocation. The replacement > for that flag would then return a struct page, as it is allowed to > actually return pages without a kernel mapping as the name suggested > (although most of the time they will actually have a kernel mapping..) > > In addition to the conversions of the existing non-coherent DMA users > the last three patches also convert the DMA coherent allocations in > the NVMe driver to use this new framework through a dmapool addition. > This was both to give me a good testing vehicle, but also because it > should speed up the NVMe driver on platforms with non-coherent DMA > nicely, without a downside on platforms with cache coherent DMA. I really wonder what is the difference between this new API and alloc_pages(GFP_DMA, n). Is this API really needed? I thought that this is legacy thing to be removed one day... Maybe it would make more sense to convert the few remaining drivers to regular dma_map_page()/dma_sync_*()/dma_unmap_page() or have I missed something? Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
