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Date:   Mon, 23 Mar 2020 18:22:56 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Joerg Roedel <joro@8bytes.org>,
        Robin Murphy <robin.murphy@arm.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct
 device
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On Mon, Mar 23, 2020 at 09:07:38PM +0530, Aneesh Kumar K.V wrote:
> 
> This is what I was trying, but considering I am new to DMA subsystem, I
> am not sure I got all the details correct. The idea is to look at the
> cpu addr and see if that can be used in direct map fashion(is
> bus_dma_limit the right restriction here?) if not fallback to dynamic
> IOMMU mapping.

I don't think we can throw all these complications into the dma
mapping code.  At some point I also wonder what the point is,
especially for scatterlist mappings, where the iommu can coalesce.