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Date:   Thu, 24 Jun 2021 15:22:23 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Oded Gabbay <oded.gabbay@gmail.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Christian =?iso-8859-1?Q?K=F6nig?= 
        <ckoenig.leichtzumerken@gmail.com>,
        Gal Pressman <galpress@amazon.com>, sleybo@amazon.com,
        linux-rdma <linux-rdma@vger.kernel.org>,
        Oded Gabbay <ogabbay@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>,
        Doug Ledford <dledford@redhat.com>,
        Tomer Tayar <ttayar@habana.ai>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Leon Romanovsky <leonro@nvidia.com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
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Subject: Re: [Linaro-mm-sig] [PATCH v3 1/2] habanalabs: define uAPI to
 export FD for DMA-BUF
Message-ID: <20210624132223.GA22258@lst.de>
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On Thu, Jun 24, 2021 at 11:52:47AM +0200, Christian K?nig wrote:
> I've already converted a bunch of the GPU drivers, but there are at least 6 
> GPU still needing to be fixed and on top of that comes VA-API and a few 
> others.
>
> What are your plans for the DMA mapping subsystem?

Building a new API that allows batched DMA mapping without the scatterlist.
The main input for my use case would be bio_vecs, but I plan to make it
a little flexible, and the output would be a list of [dma_addr,len]
tuples, with the API being flexible enough to just return a single
[dma_addr,len] for the common IOMMU coalescing case.

>
>> Btw, one thing I noticed when looking over the dma-buf instances is that
>> there is a lot of duplicated code for creating a sg_table from pages,
>> and then mapping it.  It would be good if we could move toward common
>> helpers instead of duplicating that all over again.
>
> Can you give an example?

Take a look at the get_sg_table and put_sg_table helpers in udmabuf.
Those would also be useful in armda, i915, tegra, gntdev-dmabuf, mbochs
in one form or another.

Similar for variants that use a contigous regions.