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Date:   Wed, 30 Sep 2020 18:40:23 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Paul Cercueil <paul@crapouillou.net>
Cc:     Christoph Hellwig <hch@lst.de>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Dave Airlie <airlied@linux.ie>,
        DRI <dri-devel@lists.freedesktop.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: linux-next: build failure after merge of the drm tree
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On Wed, Sep 30, 2020 at 06:39:18PM +0200, Paul Cercueil wrote:
>> dma_alloc_pages gives you cached memory, so you can't just use an
>> uncached protection for the userspace mmap here.  If you want uncached
>> memory you need to use dma_alloc_coherent paired with dma_mmap_coherent.
>> Or dma_alloc_wc for a slightly different flavor of uncached. (both
>> of the map to dma_alloc_attrs / dma_mmap_attrs eventually).
>
> I don't want uncached memory, I want non-coherent cached memory.

We don't have such a thing in the Linux API at all.