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Date:   Wed, 30 Sep 2020 15:33:13 +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>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Christoph,

Le mer. 30 sept. 2020 =E0 11:02, Christoph Hellwig <hch@lst.de> a =E9crit=20
:
> On Mon, Sep 28, 2020 at 03:31:28PM +0200, Paul Cercueil wrote:
>>  It's allocated with dma_alloc_wc, but then it's only accessed as
>>  non-coherent.
>>=20
>>  Anyway, for the time being I guess you could revert 37054fc81443.=20
>> But I
>>  have patches on top of it in drm-misc-next so it's going to be a=20
>> mess.
>>=20
>>  If we have time I can come up with a custom dumb_create() fonction,=20
>> to make
>>  sure that the GEM buffers are allocated with=20
>> dma_alloc_noncoherent(). Is
>>  there a dma_mmap_noncoherent() too?
>=20
> Please use the lower-level dma_alloc_pages and then just insert the
> pages directly using remap_pfn_range.  Although it might make sense
> to eventually create a wrapper around remap_pfn_range for all the
> vma sizing sanity checks.

One thing missing for remap_pfn_range(), I have no alternative for this:

vma->vm_page_prot =3D dma_pgprot(dev, vma->vm_page_prot,=20
DMA_ATTR_NON_CONSISTENT);

So I have to do:

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;

And that will only compile on MIPS, because these _CACHE_* macros are=20
only defined there.

I would need something like a pgprot_noncoherent(), I think.

-Paul