Re: [PATCH] dmaengine: rcar-dmac: Wait for IRQs completion when freeing channel

[Vinod Koul <vinod.koul@intel.com>]

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.

I do agree that we should add separate call to abort the txn only and use
this for abort behaviour when we want to close down..

> 
> I've talked about this in the past here:
> http://mailman.alsa-project.org/pipermail/alsa-devel/2013-October/067155.html

-- 
~Vinod