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Date: Thu, 26 Apr 2018 02:24:22 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
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Subject: Re: [Linaro-mm-sig] noveau vs arm dma ops
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On Thu, Apr 26, 2018 at 11:20:44AM +0200, Daniel Vetter wrote:
> The above is already what we're implementing in i915, at least
> conceptually (it all boils down to clflush instructions because those
> both invalidate and flush).

The clwb instruction that just writes back dirty cache lines might
be very interesting for the x86 non-coherent dma case.  A lot of
architectures use their equivalent to prepare to to device transfers.

> One architectural guarantee we're exploiting is that prefetched (and
> hence non-dirty) cachelines will never get written back, but dropped
> instead.

And to make this work you'll need exactly this guarantee.