Re: Revert "dmaengine: pl330: add DMA_PAUSE feature"

[Frank Mori Hess]

On Thu, May 17, 2018 at 1:22 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
> On 05/17/2018 06:20 PM, Frank Mori Hess wrote:
> The problem is not so much on the software side but even more so on the
> hardware side. Not all hardware even supports aborting a transfer with no
> data loss because there is no precise measurement of how much data has been
> transferred. The residue that is reported is always the lower bound, this
> much has been transferred but it might actually have been more.

I'd just like to point out, if the pl330 driver actually did report a
upper bound on the residue (lower bound on bytes transferred) that
would also blow up Marek's samsung serial driver use case.  Instead of
being in a situation where data loss might occur rarely due to a race
condition, they would be in a situation where data loss occurs every
time they stop a transfer.  Not that such a residue reporting would be
incorrect though, the pl330 driver doesn't even advertise burst level
granularity with its residue reporting.