[alsa-devel] [RFC PATCH 1/4] ALSA: core: let low-level driver or userspace disable rewinds

[Pierre-Louis Bossart]

>> Add new hw_params flag to explicitly tell driver that rewinds
>> will never be used. This can be used by low-level driver to
>> optimize DMA operations and reduce power consumption.
>> Use this flag only when data written in ring buffer will
>> never be invalidated, e.g. any update of appl_ptr is final.
>>
>> Caveat: there is currently no way to query capabilities without
>> opening a pcm stream, so applications might need to serially
>> open all exposed devices, check what they support by looking at
>> hw_params->info and close them (this is what PulseAudio does so
>> might not be an issue)
>
> The forward should also fail with such hardware, no?

The way I understand the forward is just an update of the application 
pointer without writing/reading new data, so that works. The hardware 
will just use whatever is in the ring buffer. It's weird but it would work.