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

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

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?

-- 
~Vinod