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From:   Tomasz Figa <tfiga@chromium.org>
Date:   Mon, 26 Jul 2021 13:04:53 +0900
Message-ID: <CAAFQd5D6hSoLJaBMdV-fpzn43Y6qRULR4ckejrJp_89Qpe6Xnw@mail.gmail.com>
Subject: Re: [PATCHv3 8/8] videobuf2: handle non-contiguous DMA allocations
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Dafna Hirschfeld <dafna.hirschfeld@collabora.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Ricardo Ribalda <ribalda@chromium.org>,
        Christoph Hellwig <hch@lst.de>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Collabora Kernel ML <kernel@collabora.com>
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On Mon, Jul 26, 2021 at 12:59 PM Sergey Senozhatsky
<senozhatsky@chromium.org> wrote:
>
> On (21/07/22 19:26), Dafna Hirschfeld wrote:
> > Also, the 'cookie' cb returns buf->dma_addr which is not initialized for
> > the noncontiguous api. So it is not clear how drivers should use the new api.
> > Many drivers call vb2_dma_contig_plane_dma_addr which returns the cookie.
>
> Hmm, that's a good find. Is ->dma_addr the same as what we have in
> sgt.sgl->dma_address for non-contig?

Yes. As per [1]:

"The return sg_table is guaranteed to have 1 single DMA mapped segment
as indicated by sgt->nents, but it might have multiple CPU side
segments as indicated by sgt->orig_nents."

[1] https://www.kernel.org/doc/html/latest/core-api/dma-api.html#part-ii-non-coherent-dma-allocations