linux-kernel - Re: [PATCHv3 8/8] videobuf2: handle non-contiguous DMA allocations

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Message-ID: <CAAFQd5D6hSoLJaBMdV-fpzn43Y6qRULR4ckejrJp_89Qpe6Xnw@mail.gmail.com>
Date:   Mon, 26 Jul 2021 13:04:53 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Christoph Hellwig <hch@....de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Collabora Kernel ML <kernel@...labora.com>
Subject: Re: [PATCHv3 8/8] videobuf2: handle non-contiguous DMA allocations

On Mon, Jul 26, 2021 at 12:59 PM Sergey Senozhatsky
<senozhatsky@...omium.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