On Mon, Sep 14, 2020 at 04:44:16PM +0200, Christoph Hellwig wrote:
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.
Erm ... dma_alloc_pages() returns a struct page, so is this sentence stale?
From patch 14:
+struct page *dma_alloc_pages(struct device *dev, size_t size, + dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp);
The other alternative would be to name the API dma_alloc_noncoherent, but the whole non-coherent naming seems to put people off.
You say that like it's a bad thing. I think the problem is more that people don't understand what non-coherent means and think they're supporting it when they're not.
dma_alloc_manual_flushing()?
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..)
If the page doesn't have a kernel mapping, shouldn't it return a PFN or a phys_addr?