[alsa-devel] [PATCH] ALSA: hda - delay resume haswell hdmi codec in system resume

[Lin, Mengdong]

> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Saturday, April 06, 2013 1:05 AM


> > > > Immediate playback:
> > > >   1. System skips hda_call_codec_resume and sets
> codec->resume_delayed.
> > > >   2. Process context wants to start playback, which powers up the
> > > > codec and calls intel_haswell_set_power_state.
> > > >   3. intel_haswell_wait_ready_to_resume enables unsol events and
> > > > starts to wait on ready_to_resume
> > > >   4. Gfx init finishes, and workq context fires the unsol event,
> > > > which calls hdmi_intrinsic_event, which triggers the resume_wq.
> > > >   5. Process context and workq context now continues in parallel,
> > > > potentially (but hopefully not) leading to race conditions?
> > >
> > > The current patch has a small race, but it can be avoided by
> > > clearing
> > > spec->ready_to_resume early enough, e.g. in suspend callback or in
> > > init callback, like the patch below.
> > >
> >
> > I think there is no race for Haswell. In my test I observed that the
> > unsol evnet will not be received until intel_haswell_wait_ready_to_resume()
> enables the unsol event on the pins.
> > So I put "spec->ready_to_resume = 0" before enabling the unsol event.
> 
> Practically your patch would work well, but theoretically the unsol event might
> be issued and handled by hdmi_intrinsic_event() before you go into
> intel_haswell_wait_ready_to_resume().  That is, you _clear_
> spec->ready_to_resume again and wait for the unsol event that had been
> already processed.  That's the race David pointed.
> 
> The fix is simply not to clear spec->ready_to_resume in
> intel_haswell_wait_ready_to_resume() but clear it much earlier already before
> the resume path as my patch does.  Then wait_event() passes immediately
> (and the unsol enablement of is anyway harmless).
> 

Hi Takashi,

I see. Thanks for clarifying!

I'll revise the patch and test it again when I'm in office on Monday.
Also I'll rebase the patch to for-next branch of sound git tree and fix the indentations and spaces errors.

Thanks
Mengdong