[alsa-devel] [PATCH] ALSA: hda - delay resume haswell hdmi codec in system resume
mengdong.lin at intel.com
Tue Apr 9 10:18:04 CEST 2013
> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Tuesday, April 09, 2013 3:43 PM
> To: David Henningsson
> Cc: Lin, Mengdong; alsa-devel at alsa-project.org; Girdwood, Liam R
> Subject: Re: [alsa-devel] [PATCH] ALSA: hda - delay resume haswell hdmi codec
> in system resume
> > >> I've been answering the power_save questions a little bit uncertain
> > >> so far, and that's because I don't really know. I've not
> > >> investigated power management much.
> > >>
> > >> But the person with the hardware reports that this problem happens
> > >> when on AC power only. And that makes sense with your observations
> > >> about power_save - there could very well be something that turns
> > >> power_save off when on AC power and on when on battery power.
> > >>
> > >> So, if it's just a matter of re-initializing the pin, what do you
> > >> think about this solution:
> > >>
> > >> - Resume as normal (this will enable unsol events)
> > >> - Any time an unsol event comes in, have a haswell specific
> > >> function that checks relevant pins to see that is still in D0 and
> > >> mute state correct. If not, correct it.
> > >> - This check could possibly also be done in the prepare hook for
> > >> extra safety.
> > >
> > > It won't work reliably. The problem is that the codec might be set
> > > up wrongly if it's used before the unsol event comes up. For
> > > example, a PCM resume may be performed immediately after the normal
> > > resume is finished. Meanwhile the first unsol may arrive much later than
> > Right, but if this will only mean a few samples (max 300 ms?) will
> > never reach the HDMI cable, it might be the least bad workaround.
I've tried enabling the unsol event on system resume, the unsol event will arrive in 70~80ms for HDMI and about 10ms for DP.
> It's not only about the missing few samples. The whole setup isn't reliable at
> that point, and you don't know what to re-setup for the
> *running* stream.
> > > Thus we need to delay the resume operation in anyway. And if so,
> > > there is no merit to perform the normal resume operation at the
> > > first step.
> > The normal resume operation enables unsol events, which is important,
> > otherwise we don't get the unsol notification from when the gfx
> > pipeline has finished.
> It seems that the intrinsic unsol event is always issued once when the unsol
> event is enabled, according to Intel. So, you won't miss it.
> But heck, we need more test coverage, obviously.
> > I guess the question here is how much of the codec setup is really
> > destroyed by the gfx driver? Is it just a pin in D3 and a right
> > channel mute, or is it much more that needs to be re-done after the
> > gfx driver has finished?
> I'm afraid it's too native to assume that...
Actually, we're not sure how much setting are destroyed, although it seems only the pin power state and mute status are affected.
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