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 -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
