From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: linux-sh@vger.kernel.org
Subject: Re: [PATCH] dmaengine: rcar-dmac: Wait for IRQs completion when freeing channel
Date: Thu, 15 Oct 2015 17:04:14 +0000 [thread overview]
Message-ID: <1488768.OAFyyvRcnS@avalon> (raw)
In-Reply-To: <1442233573-26684-1-git-send-email-laurent.pinchart+renesas@ideasonboard.com>
On Wednesday 14 October 2015 13:02:22 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.
Most notably audio drivers seem to call terminate_all() from a non-sleepable
context.
"We" (volunteers needed...) need to fix the API, the callers and the drivers.
In the meantime I'll resubmit this patch without making terminate_all()
synchronous to avoid introducing breakages.
--
Regards,
Laurent Pinchart
next prev parent reply other threads:[~2015-10-15 17:04 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 [this message]
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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