[PATCH v2] ASoC: rk3399_gru_sound: fix recording pop at first attempt

Mark Brown broonie at kernel.org
Sat Sep 24 11:10:42 PDT 2016

On Fri, Sep 23, 2016 at 04:27:37PM -0500, Rob Herring wrote:
> On Thu, Sep 22, 2016 at 09:50:06PM +0800, Xing Zheng wrote:
> > From: Wonjoon Lee <woojoo.lee at samsung.com>

> > Pop happens when mclk applied but dmic's own boot-time

> This statement doesn't make sense.

It is very clear if you're familiar with the problem domain - because a
DMIC is digital it's got an on/off state which means that when it
transitions from off and not outputting anything to outputting something
you get a sudden DC transition which manifests as a pop in the audio

> > Specify dmic delay times in dt to make sure
> > clocks are ready earlier than dmic working

> I don't think this really belongs in DT. Seems like better control of 
> the init order is needed. Or why not just a fixed delay in the driver?

The changelog says this is due to the DMICs having a startup time of
their own so needing a delay after they've started.  That's going to be
a system dependent thing since it'll depend on the specific component
selected and DMICs are easily interchangable.
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