[Bug 89419] [SKL][Audio][HD-A Display]: Can't detect Display audio codec if not connect HDMI and DP monitor when boot up

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89419

--- Comment #25 from Libin Yang <libin.yang at intel.com> ---
Hi Jani

(In reply to Jani Nikula from comment #24)
> (In reply to Libin Yang from comment #23)
> > As the hdmi audio can be deteced successfully when monitor is connected,
> > could you please check what's the difference gfx driver will do freom
> > monitor isn't connected?
> 
> For one, you can't expect to be able to read the registers (or the read
> values to make sense) *unless* you've called the ->get_power() function
> through the component API. There are plenty of audio registers that i915
> never touches but need the power well from i915 to operate. And you should
> expect the registers to lose their values after you ->put_power(). Check
> bspec.

For the get_power(), do you mean the power well. 

I will check whether the power well is put in audio driver side when reading
the register. Thanks.

BTW: For the detect, in audio driver, Imre has submitted the power well codec
before and I have applied the patch from Imre to enable power well on SKL
before detecting audio codec. Suppose if the audio driver is not suspended, it
will always get the power well. 

fyi, In alsa mail list, some one suggests not always powering on the power
well. Only power on it when needed. When audio will playback/capture, audio
driver will power on the power well. When gfx send unsol events, gfx will power
on the power well.

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