On Tue, Oct 16, 2012 at 12:27:55PM +0200, Hiroshi Doyu wrote:

Hi Russell,

Russell King - ARM Linux [off-list ref] wrote @ Tue, 16 Oct 2012 10:59:28 +0200:

quoted

On Tue, Oct 16, 2012 at 09:04:34AM +0300, Hiroshi Doyu wrote:

quoted

In addition to those contiguous/discontiguous page allocation, is
there any way to _import_ anonymous pages allocated by a process to be
used in dma-mapping API later?

I'm considering the following scenario, an user process allocates a
buffer by malloc() in advance, and then it asks some driver to convert
that buffer into IOMMU'able/DMA'able ones later. In this case, pages
are discouguous and even they may not be yet allocated at
malloc()/mmap().

That situation is covered.  It's the streaming API you're wanting for that.
dma_map_sg() - but you may need additional cache handling via
flush_dcache_page() to ensure that your code is safe for all CPU cache
architectures.

Remember that pages allocated into userspace will be cacheable, so a cache
flush is required before they can be DMA'd.  Hence the streaming
API.

Is the syscall "cacheflush()" supposed to be the knob for that?

Or is there any other ones to have more precise control, "clean",
"invalidate" and "flush", from userland in generic way?

No other syscalls are required - this sequence will do everything you
need to perform DMA on pages mapped into userspace:

	get_user_pages()
	convert array of struct page * to scatterlist
	dma_map_sg()
	perform DMA
	dma_unmap_sg()
	for each page in sg()
		page_cache_release(page);

If you get the list of pages some other way (eg, via shmem_read_mapping_page_gfp)
then additional maintanence may be required (though that may be a bug in
shmem - remember this stuff hasn't been well tested on ARM before.)

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