On Wed, Dec 19, 2018 at 11:44:46PM +0200, Dimitris Papavasiliou wrote: > On 12/19/18 6:19 PM, Mark Brown wrote: > > If you're saying you're keeping the device open while you're doing this > > (rather than closing the stream and reconfiguring) then I'd expect > > you're going to find other hardware which has similar issues, reclocking > > the device isn't something I'd expect to be able to do glitch free. > I got pops even if I opened the stream, called hw_params and closed it > on each iteration, but, as it turns out, that was in part because I > was being lazy, using a Python script to do the above, which sneaked > in a hw_params call immediately after opening the stream, to "reset" > it to default values. Wow, that's... interesting. > So I've retried your suggested approach. It looks like setting > .ignore_pmdown_time = 1 in the snd_soc_dai_link of the machine driver > is enough to cause immediate power ups/downs, but I get the following > behavior: The device gets powered up immediately after the first > hw_params call (even if nothing gets played subsequently) and it gets Are you sure it's the hw_params() call itself? > powered down immediately after it's closed. This does avoid the pop > when the device gets configured right after opening it, which, as you > say, seems to be what usually happens (I checked with the SoX play > utility and the MPD), but a pop is generated if there are multiple > hw_params calls and the sample rate is changed in any but the first one > (where the device is still powered down). > This can conceivably happen (for instance the Python library I was > using, forces you to make multiple hw_params calls, in order to set > more than one parameters). Is there some way to configure the DAPM to > power up the card right before playback starts, and power it down > right after it stops? This would prevent pops even in such > pathological cases. This is what's supposed to happen. DAPM is triggered in the prepare() callback, you can call hw_params() as often as you like and it should have no interaction with DAPM at all.
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