[alsa-devel] Master Plan on rewinding

[Alexander E. Patrakov]

22.09.2014 19:20, Lars-Peter Clausen wrote:
>>
>> Does this mean the those sound card can report
>> DMA_RESIDUE_GRANULARITY_BURST and driver use readl in pcm pointer
>> callback ?
>>
>> A few PCI sound cards use SG buffer including hda
>>
>> It seem that pulseaudio expect the driver support
>> DMA_RESIDUE_GRANULARITY_BURST for rewind/ timer scheduling
>
> Yes. This is why we set the BATCH flag if the granularity is not
> DMA_RESIDUE_GRANULARITY_BURST so for example pulse audio can disable
> timer scheduling.

For the record, disabling timer-based scheduling is IMHO a matter of 
further discussion. As long as there is enough safeguard, I think that 
timer-based scheduling can still be used, and is useful. A living proof 
is the whole story with the snd-usb-audio driver where (justified) 
addition of the BATCH flag was perceived as a performance regression and 
not as a fix to some real and obvious problem.

I do agree that such devices need to be marked up with the BATCH flag, 
so that PulseAudio chooses reasonable hardware parameters.

-- 
Alexander E. Patrakov