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    SubjectRe: [PATCH] [media] vb2: map dmabuf for planes on driver queue instead of vidioc_qbuf
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    Hello Hans, Michael and Marek,

    Thanks a lot for your feedback.

    On 07/18/2016 04:34 AM, Hans Verkuil wrote:
    > On 07/15/2016 06:26 PM, Javier Martinez Canillas wrote:
    >> The buffer planes' dma-buf are currently mapped when buffers are queued
    >> from userspace but it's more appropriate to do the mapping when buffers
    >> are queued in the driver since that's when the actual DMA operation are
    >> going to happen.
    >
    > Does this solve anything? Once the DMA has started the behavior is the same
    > as before (QBUF maps the dmabuf), only while the DMA engine hasn't started
    > yet are the QBUF calls just accepted and the mapping takes place when the
    > DMA is kickstarted. This makes QBUF behave inconsistently.
    >
    > You don't describe here WHY this change is needed.
    >

    Nicolas pointed me to the TODO and suggested me the patch for the reasons
    he explained in his latest email. And yes, this should had been tagged as
    a RFC and just to know what you think about it. Sorry for missing that.

    > I'm not sure I agree with the TODO, and even if I did, I'm not sure I agree
    > with this solution. Since queuing the buffer to the driver is not the same
    > as 'just before the DMA', since there may be many buffers queued up in the
    > driver and you don't know in vb2 when the buffer is at the 'just before the DMA'
    > stage.
    >

    Right, I meant "as closer as possible to when the actual DMA is going to happen"
    rather than "just before the DMA".

    > Regards,
    >
    > Hans
    >

    Best regards,
    --
    Javier Martinez Canillas
    Open Source Group
    Samsung Research America

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