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    SubjectRe: Revert "dmaengine: pl330: add DMA_PAUSE feature"
    On 15-05-18, 11:50, Frank Mori Hess wrote:
    > On Tue, May 15, 2018 at 2:21 AM, Vinod <vkoul@kernel.org> wrote:
    > >
    > > For Pause/resume data loss is _not_ expected.
    > >
    > >> > and some of the 8250 drivers like 8250_dw.c set a maxburst > 1. If it
    > >> > can't count on the pause/residue/terminate working without data loss
    > >> > then it is just broken. As is the 8250_omap.c driver. Is the
    > >> > description of dmaengine_pause in the documentation of "This pauses
    > >> > activity on the DMA channel without data loss" to be interpreted as
    > >> > "as long as you resume afterwards"?
    > >>
    > >> I assume that this requirement is for both - resuming and terminating.
    > >
    > > Terminate is abort, data loss may happen here.
    >
    > Wait, are you saying if you do
    >
    > dma pause

    no data loss
    > read residue

    here as well
    > dma terminate

    Oh yes, we aborted...
    >
    > then it is acceptable for there to be data loss, because it can be
    > blamed on the terminate? In that case the usage of dmaengine in all
    > the 8250 serial drivers is broken. Every time there is a break in the
    > incoming rx data, the 8250 driver does pause/residue/terminate which
    > could potentially cause data from the incoming data stream to be
    > dropped.

    As I said terminate is abort. It cleans up the channel and is supposed to
    used for cleanup not for stopping. See Documentation:

    - device_terminate_all

    - Aborts all the pending and ongoing transfers on the channel

    - For aborted transfers the complete callback should not be called

    - Can be called from atomic context or from within a complete
    callback of a descriptor. Must not sleep. Drivers must be able
    to handle this correctly.

    - Termination may be asynchronous. The driver does not have to
    wait until the currently active transfer has completely stopped.
    See device_synchronize.

    Thanks
    --
    ~Vinod

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