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

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Message-ID: <YP41zzARXEXESEXE@google.com>
Date:   Mon, 26 Jul 2021 13:10:55 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        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 (21/07/26 13:04), Tomasz Figa wrote:
> 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."

Thanks. So the fix can look as follows:

---

static int vb2_dc_alloc_non_coherent(struct vb2_dc_buf *buf)
{
        struct vb2_queue *q = buf->vb->vb2_queue;

        buf->dma_sgt = dma_alloc_noncontiguous(buf->dev,
                                               buf->size,
                                               buf->dma_dir,
                                               GFP_KERNEL | q->gfp_flags,
                                               buf->attrs);
        if (!buf->dma_sgt)
                return -ENOMEM;

+        buf->dma_addr = sg_dma_address(buf->dma_sgt->sgl);

---