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Date:   Wed, 30 Sep 2020 18:39:18 +0200
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: linux-next: build failure after merge of the drm tree
To:     Christoph Hellwig <hch@lst.de>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Dave Airlie <airlied@linux.ie>,
        DRI <dri-devel@lists.freedesktop.org>,
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Le mer. 30 sept. 2020 =E0 18:11, Christoph Hellwig <hch@lst.de> a =E9crit=20
:
> On Wed, Sep 30, 2020 at 03:33:13PM +0200, Paul Cercueil wrote:
>>  One thing missing for remap_pfn_range(), I have no alternative for=20
>> this:
>>=20
>>  vma->vm_page_prot =3D dma_pgprot(dev, vma->vm_page_prot,
>>  DMA_ATTR_NON_CONSISTENT);
>>=20
>>  So I have to do:
>>=20
>>  vma->vm_page_prot =3D pgprot_noncached(vma->vm_page_prot);
>>  pgprot_val(vma->vm_page_prot) &=3D ~_CACHE_MASK;
>>  pgprot_val(vma->vm_page_prot) |=3D _CACHE_CACHABLE_NONCOHERENT;
>>=20
>>  And that will only compile on MIPS, because these _CACHE_* macros=20
>> are only
>>  defined there.
>>=20
>>  I would need something like a pgprot_noncoherent(), I think.
>=20
> 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=20
> 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.

-Paul