Re: [PATCH v4 2/3] common: DMA-mapping: add DMA_ATTR_NOHUGEPAGE attribute

[Russell King - ARM Linux]

On Fri, Jan 08, 2016 at 03:05:13PM -0800, Doug Anderson wrote:
> 1. I have to go and touch all existing DMA-mapping code to set
> DMA_ATTR_HUGE_PAGE.  That will be a big patchset and touch more code,
> making it more likely to break something.
...

Indeed, I was actually thinking of a positive "prefer/only use/force
smaller pages" thing rather than "allow huge pages" as a way to get
rid of the "no huge pages" negative as a way to get around that.
It has the same meaning when set as DMA_ATTR_NO_HUGE_PAGE but
avoids the problem of wondering what

	!dma_get_attr(DMA_ATTR_NO_HUGE_PAGE, attrs)

means.

I wasn't thinking of DMA_ATTR_HUGE_PAGE as that would certainly be
wrong when CONFIG_HAVE_DMA_ATTRS is disabled (when dma_get_attr()
always returns 0.)

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