[alsa-devel] HD-audio runtime PM

[Lin, Mengdong]

> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Tuesday, December 10, 2013 10:26 PM

> > > > HW team clarified that HDMI/DP jack insertion cannot wake up the
> > > controller from D3. So this is a HW restriction for Haswell, not a
> > > driver regression.
> > > >
> > > > Now the problem on Haswell/Broadwell is:
> > > > After the controller enters D3, Gfx driver can still detect
> > > > HDMI/DP hot
> > > plug event even if the display power well is disabled.
> > > > Although Gfx driver set Presence Detect and ELD Valid , the audio
> > > controller does not wake up and so audio driver has no idea about
> > > the HDMI/DP hot-plug.
> > > >
> > > > Is it audio driver itself or the user space that need this ELD info?
> > > > Maybe Gfx driver can directly report ELD info to user space.
> > >
> > > If so, the graphics driver can wake up the audio driver as well --
> > > this is yet one more reason to create a direct communication channel
> > > between the graphics and audio drivers :)
> >
> > Need the audio driver provide an API for gfx driver?
> > Maybe this API can call snd_hda_power_up(codec) and then
> > snd_hda_power_down(codec), thus the controller and codec will wake
> up and audio driver can check ELD info.
> 
> Well, we can create a common object containing the ops registered by
> both graphics and audio drivers, then communicate through it, something
> like vga_switcheroo.

Hi Takashi,

I'm sure how to use a common object like vga_switcheroo. Would you please share more info?

I feel a wake up process may be like this:
- Gfx driver detects the hot-plug at first and notify audio driver by the communication channel.
- In the notification callback, the audio driver wakes up the audio controller to D0, but codec can still stay in D3. 
 (Hope we can add a time out for controller here to avoid controller back to D3 at once and lose the capability to check unsol event)
- Then when Gfx driver enables or disables audio, and the audio controller can receive the unsol event in D0.
- Audio driver check ELD in unsol event handler, this will make codec resume to D0.

Regards
Mengdong