From: Lars-Peter Clausen <lars@metafoo.de>
To: linux-sh@vger.kernel.org
Subject: Re: [PATCH] dmaengine: rcar-dmac: Wait for IRQs completion when freeing channel
Date: Fri, 16 Oct 2015 13:47:54 +0000 [thread overview]
Message-ID: <5621000A.90708@metafoo.de> (raw)
In-Reply-To: <1442233573-26684-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com>
On 10/15/2015 07:09 PM, Laurent Pinchart wrote:
> Hi Lars,
>
> On Thursday 15 October 2015 09:35:31 Lars-Peter Clausen wrote:
>> On 10/15/2015 05:56 AM, Vinod Koul wrote:
>>> On Wed, Oct 14, 2015 at 01:02:22PM +0200, Lars-Peter Clausen wrote:
>>>> On 10/14/2015 12:50 PM, Vinod Koul wrote:
>>>>> On Thu, Oct 08, 2015 at 04:51:30PM +0200, Lars-Peter Clausen wrote:
>>>>>>> The DMA engine API states that
>>>>>>>
>>>>>>> * device_terminate_all
>>>>>>>
>>>>>>> - Aborts all the pending and ongoing transfers on the channel
>>>>>>> - This command should operate synchronously on the channel,
>>>>>>> terminating right away all the channels
>>>>>>>
>>>>>>> I wonder how to interpret "synchronously" here, should terminate_all()
>>>>>>> wait for termination to be complete ? In that case it wouldn't be
>>>>>>> valid to call it from non-sleepable context.
>>>>>>
>>>>>> We need to extend the DMAengine API to allow synchronization. The issue
>>>>>> is not only the IRQ itself but also the tasklet that can be scheduled
>>>>>> from the IRQ. Since we in some cases (e.g. audio underrun) call
>>>>>> terminate_all() from within the completion callback that runs in the in
>>>>>> the tasklet we can't synchronize to the tasklet in
>>>>>> dmaengine_terminate_all(). We need a separate API call to handle this.
>>>>>> And then maybe have a helper like dmaengine_terminate_all_sync() that
>>>>>> terminates and synchronizes. And in cases where terminate_all is called
>>>>>> from a context where it can't synchronize the new API needs to be
>>>>>> called separately before freeing the resources.
>>>>>
>>>>> Right now the terminate_all() is intended for syncronous behaviour which
>>>>> prevents it from being invoked in the callback.
>>>>
>>>> That does not match reality though. Which means the documentation is
>>>> wrong. Pretty much all drivers implement a non-synchronous terminate
>>>> function and there are users that rely on this.
>>>
>>> Lets fix that then :)
>>>
>>> We should have both option IMHO, as I think we have both types of
>>> usages... Care to send a patch?
>>
>> Yeah, it's on my TODO list for the next month, since I need the synchronous
>> terminate elsewhere as well.
>
> The DMA engine API needs lots of love. Should we try to synchronize on all the
> open issues to define a coherent direction ?
Sure. Stuff I have on my wish list:
* Better status reporting on completed transfers. Errors,
underflow/overflow, number of bytes transferred.
* Support for making all transfers cyclic. Most controllers support this
but it is currently not exposed through the API. This is e.g. useful for
video (cyclic 2d transfers) as well as audio when we do not want to or can
not use a continuous buffer.
- Lars
prev parent reply other threads:[~2015-10-16 13:47 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-14 12:26 [PATCH] dmaengine: rcar-dmac: Wait for IRQs completion when freeing channel Laurent Pinchart
2015-09-15 0:11 ` Kuninori Morimoto
2015-10-05 14:11 ` Vinod Koul
2015-10-08 14:22 ` Laurent Pinchart
2015-10-08 14:51 ` Lars-Peter Clausen
2015-10-14 10:47 ` Vinod Koul
2015-10-14 11:02 ` Lars-Peter Clausen
2015-10-15 3:52 ` Vinod Koul
2015-10-15 7:35 ` Lars-Peter Clausen
2015-10-15 17:04 ` Laurent Pinchart
2015-10-15 17:09 ` Laurent Pinchart
2015-10-15 17:15 ` Lars-Peter Clausen
2015-10-16 13:47 ` Lars-Peter Clausen [this message]
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