Subject: Re: [PATCH 0/6] drm+dma: cache support for arm, etc

From: Christoph Hellwig <[email-masked]>
Date: Thu, 15 Aug 2019 20:52:00 +0200

On Thu, Aug 15, 2019 at 06:48:39PM +0000, Koenig, Christian wrote:
> Well, for the graphics case I absolutely need to keep the linear kernel mapping. Because for certain use cases the memory is accessed by the kernel all the time as well.

Then don't set DMA_ATTR_NO_KERNEL_MAPPING.  At least for x86 and arm64
we should be able to support uncached allocations easily even without
that, and I plan to support that for your use case.  But if the driver
is explicitly saying it doesn't want a permanent kernel mapping it makes
sense to (optionally if the architecture can easily do it) unmap the
memory from the kernel linear mapping.

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