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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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