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    SubjectRe: [PATCHv5] DMAEngine: Define interleaved transfer request api
    2011/10/14 Vinod Koul <vinod.koul@intel.com>:
    > On Fri, 2011-10-14 at 22:55 +0800, Barry Song wrote:
    >> Hi Vinod,
    >>
    >> 2011/10/14 Vinod Koul <vinod.koul@intel.com>:
    >> > On Fri, 2011-10-14 at 17:21 +0530, Jassi Brar wrote:
    >> >> On 14 October 2011 13:02, Barry Song <21cnbao@gmail.com> wrote:
    >> >> >
    >> >> > what if i want a cyclic interleaved transfer? i think the cyclic
    >> >> > interleaved transfer is what i want for audio dma.
    >> >> >
    >> >> ... we need to restore 'bool frm_irq' and add new 'bool cyclic' that
    >> >> would replay the transfer(i.e, reset dma-pointers to src_start & dst_start)
    >> >> after 'numf' frames have been transferred.
    >> > I was thinking more on lines to have this conveyed thru a flag.
    >> >
    >> > Anyway I plan to work on merging device_prep_slave_sg and
    >> > device_prep_cyclic to single API. Think more of device_prep_cyclic as
    >> > special case with sg length one and flag to tell dmac its cyclic.
    >> >
    >> > Similarly here we could use/define this flag to say this transfer is
    >> > also cyclic in nature and dmac then reloads the list again.
    >> > That way any prep can be made cyclic in nature by just using this flag.
    >> >
    >> > @Barry: Why would you need to use interleaved API for audio?
    >>
    >> At first, audio dma is typically cyclic. if no underflow and overflow
    >> happens, it will always be running. underflow and overflow will
    >> trigger the cyclic dma termination.
    > Yes and you terminate dma. Then prepare will be called again and you
    > setup DMA again and on trigger start you start DMA again.
    > No need for interleaving in this case.
    >>
    >> in case audio PCM data is interleaved and saved in dma buffer  as below:
    >>
    >> left (2B)  right (2B)  left (2B)  right (2B)   left (2B)  right (2B)
    >> left (2B)  right (2B)
    >> left (2B)  right (2B)  left (2B)  right (2B)   left (2B)  right (2B)
    >> left (2B)  right (2B)
    >> left (2B)  right (2B)  left (2B)  right (2B)   left (2B)  right (2B)
    >> left (2B)  right (2B)
    >> left (2B)  right (2B)  left (2B)  right (2B)   left (2B)  right (2B)
    >> left (2B)  right (2B)
    >> ,,,,
    >>
    >> and some hardwares need two seperate dma channels to tranfer left and
    >> right audio channel.
    >>
    >> For 1st and 2nd dma channel, they want dma address increases 4bytes
    >> and transfer 2bytes every line.
    >> so it looks to me like a cyclic interleaved dma.
    > Hmmm, do we have sound cards which use this?
    > Nevertheless for this kind of transfers we would need interleaved cyclic
    > DMA as well, Do you have such usage? Can you tell me which codec
    > requires this?

    Vinod, actually it is not decided by codec. it is only related with
    the hardware of pcm, i2s or AC'97 controllers in SoC. i did remember
    some people once licensed a TDM tranfer enginee from synopsys and IC
    guys bound one TDM slot, which has a seperate dma channel, to one
    audio channel then organize several TDM slots into a AC97 controller.

    i am on holiday now and i can't give you more information until next week.

    Still i saw most other chips binding multi-channels of an I2S/PCM/AC97
    audio controller in a dma channel, then it doesn't need interleaved
    dma api as its dma address will increase continuously. dma will
    transfer left+right together but not one left and one right.

    >
    >
    > --
    > ~Vinod

    -barry
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