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: Thu, 15 Oct 2015 07:35:31 +0000 [thread overview]
Message-ID: <561F5743.1090501@metafoo.de> (raw)
In-Reply-To: <1442233573-26684-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com>
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.
next prev parent reply other threads:[~2015-10-15 7:35 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 [this message]
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
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