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Date:   Wed, 2 May 2018 14:41:51 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Michel =?iso-8859-1?Q?D=E4nzer?= <michel@daenzer.net>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Christoph Hellwig <hch@lst.de>,
        iommu@lists.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] swiotlb: Fix inversed DMA_ATTR_NO_WARN test
Message-ID: <20180502124151.GA22857@lst.de>
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On Wed, May 02, 2018 at 02:18:56PM +0200, Daniel Vetter wrote:
> Other dma-api backends like cma just shut up when __GFP_NOWARN is
> passed. And afaiui Christoph Hellwig has plans to nuke the DMA_ATTR
> stuff (or at least clean it up) - should we just remove
> DMA_ATTR_NO_WARN and instead only look at __GFP_NOWARN?

No.  __GFP_NOWARN (and gfp_t flags in general) are the wrong interface
for dma allocations and just cause problems.  I actually plan to
get rid of the gfp_t argument in dma_alloc_attrs sooner, and only
allow either GFP_KERNEL or GFP_DMA passed in dma_alloc_coherent.

> Or maybe we should at least enforce that both or none are set, for
> consistency for now?

The interface should be DMA_ATTR_NO_WARN.  __GFP_NOWARN in this
context was never documented, and just slipped in.