Re: [alsa-devel] Can DMA address, periods, buffer size, etc change after hw_params is called?

Hans-Christian Egtvedt wrote:

Is there a chance that the following might happen:

• stop trigger,
• hw_free
• hw_params
• prepare
• start trigger

I.e. without calling close and open?

Yes.

It is also possible that the same happens without hw_free, i.e., hw_params has to initialize _or_ to change the parameters.

Clemens Ladisch clemens@ladisch.de wrote:

...

The DMA address is selected by the driver in the hw_params callback, but most drivers let the framework handle this by calling snd_pcm_lib_malloc_pages().

Yes, this is what I do today. I am considering if I should release the DMA stuff in hw_free and then in the prepare callback check if it needs to be prepared again (since it was released in hw_free).

The framework guarantees that prepare is called only when the hardware parameters are set.

Best regards, Clemens