Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

[FUJITA Tomonori]

On Tue, 13 Jul 2010 09:20:12 +0100
Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:

> > Why video4linux can't use the DMA API? Doing DMA with vmalloc'ed
> > buffers is a thing that we should avoid (there are some exceptions
> > like xfs though).
> 
> Vmalloc is about the only API for creating virtually linear memory areas.
> The video stuff really needs that to avoid lots of horrible special cases
> when doing buffer processing and the like.
> 
> Pretty much each driver using it has a pair of functions 'rvmalloc' and
> 'rvfree' so given a proper "vmalloc_for_dma()" type interface can easily
> be switched

We already have helper functions for DMA with vmap pages,
flush_kernel_vmap_range and invalidate_kernel_vmap_range.

I think that the current DMA API with the above helper functions
should work well drivers that want virtually linear large memory areas
(such as xfs).
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