From: robert.jarzmik@free•fr (Robert Jarzmik)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v4 1/4] dma: mmp_pdma: only complete one transaction from dma_do_tasklet()
Date: Sun, 25 Aug 2013 03:15:09 +0200 [thread overview]
Message-ID: <878uzqr2oy.fsf@free.fr> (raw)
In-Reply-To: <52131E40.5040304@gmail.com> (Daniel Mack's message of "Tue, 20 Aug 2013 09:44:00 +0200")
Daniel Mack <zonque@gmail•com> writes:
> Hi Xiang,
>
> On 20.08.2013 04:27, Xiang Wang wrote:
>> I think we would not run into the situation that there is a descriptor
>> with ENDIRQEN set in the middle of the running chain.
>>
>> in mmp_pdma.c:
>> mmp_pdma_tx_submit() -> append_pending_queue() ->
>> tail->desc.dcmd &= ~DCMD_ENDIRQEN;
>>
>> So in the pending list (same for running list), only the last descriptor
>> will have ENDIRQEN set.
>
> Right, thanks for noting that.
>
> But is that what we want? I think that clearing of the ENDIRQEN bit
> needs to be removed then, because if we really have multiple
> transactions running, then we want to get an interrupt whenever _any_ of
> it is completed.
At least that's something pxa_camera.c needs, ie. have the dma interrupt handler
called as soon as the _first_ of many transactions queued on the same channel is
finished.
This is necessary to declare the video capture buffer as "done", which is
signaled by a terminated DMA transaction. And of course, in video recording,
another one is beginning on the channel, while the finished video buffer can be
safely unmapped and handed over to userland.
> Hence, would you agree that we should remove that "tail->desc.dcmd &=
> ~DCMD_ENDIRQEN;" modification in order to make the above logic work?
Same question on my side.
My understanding is that the current bebaviour violates the dmaengine
specification (Documentation/dmaengine.txt, chapter 5, "On completion of each
DMA operation, the next in queue is started and a tasklet triggered. The tasklet
will then call the client driver completion callback routine for notification,
if set.)
Cheers.
--
Robert
next prev parent reply other threads:[~2013-08-25 1:15 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-16 17:05 [PATCH v4 0/4] dma: pdma: cyclic, residue, DMA_PRIVATE Daniel Mack
2013-08-16 17:05 ` [PATCH v4 1/4] dma: mmp_pdma: only complete one transaction from dma_do_tasklet() Daniel Mack
2013-08-20 2:27 ` Xiang Wang
2013-08-20 7:44 ` Daniel Mack
2013-08-25 1:15 ` Robert Jarzmik [this message]
2013-08-16 17:05 ` [PATCH v4 2/4] dma: mmp_pdma: add support for cyclic DMA descriptors Daniel Mack
2013-08-16 17:05 ` [PATCH v4 3/4] dma: mmp_pdma: add support for residue reporting Daniel Mack
2013-08-21 11:35 ` Xiang Wang
2013-08-21 11:52 ` Andy Shevchenko
2013-08-21 12:03 ` Daniel Mack
2013-08-21 12:08 ` Andy Shevchenko
2013-08-25 16:11 ` Vinod Koul
2013-08-25 17:01 ` Russell King - ARM Linux
2013-08-25 16:48 ` Vinod Koul
2013-08-25 18:06 ` Russell King - ARM Linux
2013-08-26 6:07 ` Robert Jarzmik
2013-08-21 11:55 ` Daniel Mack
2013-08-16 17:05 ` [PATCH v4 4/4] dma: mmp_pdma: set DMA_PRIVATE Daniel Mack
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