Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

Is dma_common_contiguous_remap() still necessary in the
DMA_ATTR_NON_CONSISTENT case? I would presume it would be fine to just
return a linearly mapped address in that case.

On Mon, Aug 05, 2019 at 07:55:44PM -0700, Gavin Li wrote:

quoted

        /* create a coherent mapping */
        ret = dma_common_contiguous_remap(page, size, VM_USERMAP,
-                       arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs),
+                       dma_pgprot(dev, PAGE_KERNEL, attrs),
                        __builtin_return_address(0));
        if (!ret) {
                __dma_direct_free_pages(dev, size, page);

Is dma_common_contiguous_remap() still necessary in the
DMA_ATTR_NON_CONSISTENT case? I would presume it would be fine to just
return a linearly mapped address in that case.

It would not be required for a real DMA_ATTR_NON_CONSISTENT
implementation.  But only parisc and mips actually properly implement
DMA_ATTR_NON_CONSISTENT, everyone ignores it.  Given that the API is
a little ill defined and I have a better replacement in the pipeline
I don't want to start implementing it for other architectures now.