Will ALSA ever call _prepare or _hw_params while it's playing?

Will ALSA ever call _prepare or _hw_params while it's playing?

[Timur Tabi]

I have an ASoC driver with a _hw_params, _prepare, and _trigger functions.  I've
recently discovered that I need to keep one of my devices disabled until
playback starts.

So I would like to know if ALSA will ever call _hw_params, _prepare, or _startup
if playback or capture is currently in process, or will ALSA first call the
_trigger to stop/pause the driver.

If ALSA does stop/pause the driver before changing parameters, then I can safely
assume the device is always disabled during those functions.

-- 
Timur Tabi
Linux kernel developer at Freescale

Re: Will ALSA ever call _prepare or _hw_params while it's playing?

[Clemens Ladisch]

Timur Tabi wrote:
> I have an ASoC driver with a _hw_params, _prepare, and _trigger functions.  I've
> recently discovered that I need to keep one of my devices disabled until
> playback starts.
>
> So I would like to know if ALSA will ever call _hw_params, _prepare, or _trigger
> if playback or capture is currently in process, or will ALSA first call the
> _trigger to stop/pause the driver.

While a stream is running (after trigger with START), ALSA will only
call the pointer or the trigger (STOP/PAUSE/SUSPEND) callbacks.

Different streams are not synchronized in any way.  (This also applies to
the playback/capture streams of one card.)


Regards,
Clemens

Re: Will ALSA ever call _prepare or _hw_params while it's playing?

[Timur Tabi]

Clemens Ladisch wrote:
> Timur Tabi wrote:
>> I have an ASoC driver with a _hw_params, _prepare, and _trigger functions.  I've
>> recently discovered that I need to keep one of my devices disabled until
>> playback starts.
>>
>> So I would like to know if ALSA will ever call _hw_params, _prepare, or _trigger
>> if playback or capture is currently in process, or will ALSA first call the
>> _trigger to stop/pause the driver.
> 
> While a stream is running (after trigger with START), ALSA will only
> call the pointer or the trigger (STOP/PAUSE/SUSPEND) callbacks.

That's good.

> Different streams are not synchronized in any way.  (This also applies to
> the playback/capture streams of one card.)

Ah, I hadn't thought about that.  If I'm doing simultaneous capture and playback
through the same device, then I can't guarantee that it's disabled.  Argh.

Thanks.

-- 
Timur Tabi
Linux kernel developer at Freescale