Re: [PATCH v1] dmaengine: tegra-apb: Handle DMA_PREP_INTERRUPT flag properly

[Dmitry Osipenko]

08.05.2019 12:24, Jon Hunter ÐÐÑÐÑ:
> 
> On 05/05/2019 19:12, Dmitry Osipenko wrote:
>> The DMA_PREP_INTERRUPT flag means that descriptor's callback should be
>> invoked upon transfer completion and that's it. For some reason driver
>> completely disables the hardware interrupt handling, leaving channel in
>> unusable state if transfer is issued with the flag being unset. Note
>> that there are no occurrences in the relevant drivers that do not set
>> the flag, hence this patch doesn't fix any actual bug and merely fixes
>> potential problem.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> 
> From having a look at this, I am guessing that we have never really
> tested the case where DMA_PREP_INTERRUPT flag is not set because as you
> mentioned it does not look like this will work at all!
> 
> Is there are use-case you are looking at where you don't set the
> DMA_PREP_INTERRUPT flag?

No. I just noticed it while was checking whether we really need to
handle the BUSY bit state for the Ben's "accurate reporting" patch.

> If not I am wondering if we should even bother supporting this and warn
> if it is not set. AFAICT it does not appear to be mandatory, but maybe
> Vinod can comment more on this.

The warning message will be also okay if it's not mandatory.