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Date:   Mon, 28 Sep 2020 13:46:55 +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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In-Reply-To: <20200928113415.GA555@lst.de>
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        <20200928060427.GA15041@lst.de> <KU5DHQ.C9RVOLP69UO81@crapouillou.net>
        <20200928113415.GA555@lst.de>
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Le lun. 28 sept. 2020 =E0 13:34, Christoph Hellwig <hch@lst.de> a =E9crit=20
:
> On Mon, Sep 28, 2020 at 12:15:56PM +0200, Paul Cercueil wrote:
>>  Hi Christoph,
>>=20
>>  Le lun. 28 sept. 2020 =E0 8:04, Christoph Hellwig <hch@lst.de> a=20
>> =E9crit :
>>>  On Mon, Sep 28, 2020 at 01:54:05PM +1000, Stephen Rothwell wrote:
>>>>   Hi all,
>>>>=20
>>>>   After merging the drm tree, today's linux-next build (x86_64
>>>>  allmodconfig)
>>>>   failed like this:
>>>=20
>>>  The driver needs to switch do dma_alloc_noncoherent +=20
>>> dma_sync_single*
>>>  like the other drivers converted in the dma tree.  Paul, let me=20
>>> know if
>>>  you have any questions.
>>=20
>>  I don't dma_alloc* anything, DRM core does. I use the
>>  DMA_ATTR_NON_CONSISTENT attr with dma_mmap_attrs(). Is there a=20
>> replacement
>>  for that?
>=20
> dma_mmap_attrs can only be used on allocations from dma_mmap_attrs=20
> with
> the same attrs.  As there is no allocation using=20
> DMA_ATTR_NON_CONSISTENT
> in the drm core, something looks very fishy here.

Is that a fact? I don't see why you couldn't change the cache settings=20
after allocation. In practice it works just fine.

> Where does the allocation you try to mmap come from?  All the=20
> allocations
> in drivers/gpu/drm/drm_gem_cma_helper.c seems to use dma_alloc_wc (aka
> dma_allloc_attrs with the DMA_ATTR_WRITE_COMBINE flag).

It's the dma_alloc_wc.

-Paul