linux-kernel - Re: linux-next: build failure after merge of the drm tree

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Date:   Wed, 30 Sep 2020 18:45:02 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Christoph Hellwig <hch@....de>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Dave Airlie <airlied@...ux.ie>,
        DRI <dri-devel@...ts.freedesktop.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the drm tree



Le mer. 30 sept. 2020 à 18:40, Christoph Hellwig <hch@....de> a écrit 
:
> 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.

dma_pgprot(dev, vma->vm_page_prot, DMA_ATTR_NON_CONSISTENT);

That was giving me non-coherent cached memory, and now I don't have an 
alternative.

-Paul