[Sound-open-firmware] [PATCH] sof: Turn IRQs off globally when send command to pipeline component

[Liam Girdwood]

On Tue, 2018-03-27 at 10:37 -0500, Pierre-Louis Bossart wrote:
> On 3/27/18 4:17 AM, Wu Zhigang wrote:
> > When pipeline processing the command, we have to turn off the IRQs.
> > If not, the DMA IRQ will interrupt the pipeline state set process,
> > when pipeline is scheduled, the states inconsistence will cause xrun.
> 
> we disable the irqs but then will walk the graph from host to DAI with 
> component_op_downstream to pass a COMPS_OPS_CMD with in turn will call 
> all .cmd callbacks from all components
> 
> This could take a significant amount of time and lead to interrupts 
> unrelated to that specific pipeline not being serviced, leading to xruns.
> 
> what am I missing?
> 

The pipeline cmd just walks the pipeline and updates the component state
alongside calling comp_cmd() on each component (START, STOP, PAUSE etc). This is
very fast in practice, about 20us on BYT. I agree that we do need to be clear
this is in atomic context (like ALSA trigger) and that any component de-
init/cleanup must be done in comp_reset().

I will be writing some docs to go alongside 1.2 so I can include this in the
programming documentation.

Liam