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Date:   Mon, 17 Feb 2020 00:01:38 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     "Isaac J. Manjarres" <isaacm@codeaurora.org>
Cc:     iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Liam Mark <lmark@codeaurora.org>, joro@8bytes.org,
        pratikp@codeaurora.org, kernel-team@android.com
Subject: Re: [RFC PATCH] iommu/dma: Allow drivers to reserve an iova range
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On Fri, Feb 14, 2020 at 02:58:16PM -0800, Isaac J. Manjarres wrote:
> From: Liam Mark <lmark@codeaurora.org>
> 
> Some devices have a memory map which contains gaps or holes.
> In order for the device to have as much IOVA space as possible,
> allow its driver to inform the DMA-IOMMU layer that it should
> not allocate addresses from these holes.

Layering violation.  dma-iommu is the translation layer between the
DMA API and the IOMMU API.  And calls into it from drivers performing
DMA mappings need to go through the DMA API (and be documented there).