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

[Takashi Iwai <tiwai@suse.de>]

At Fri, 05 Apr 2013 15:01:47 +0200,
Takashi Iwai wrote:
> 
> At Tue, 02 Apr 2013 14:49:40 +0200,
> David Henningsson wrote:
> > 
> > On 04/02/2013 02:18 PM, Takashi Iwai wrote:
> > > At Tue, 02 Apr 2013 13:53:16 +0200,
> > > David Henningsson wrote:
> > >>
> > >> On 03/27/2013 11:01 AM, Lin, Mengdong wrote:
> > >>>> -----Original Message-----
> > >>>> From: David Henningsson [mailto:david.henningsson@canonical.com]
> > >>>> Sent: Wednesday, March 27, 2013 4:19 PM
> > >>>
> > >>>>> The Haswell codec set_power_state ops (intel_haswell_set_power_state) will
> > >>>> only wait if this is a delayed resume and clear this flag after waiting. And
> > >>>> actually, there is no waiting even in this case. Because when 1st user operation
> > >>>> after system resume happens, Gfx already finishes resuming and audio
> > >>>> initialization, so as long as intel_haswell_wait_ready_to_resume() enable the
> > >>>> unsol event, the unsol event comes and so so waiting finishes. The 300ms time
> > >>>> out is set for safety consideration in case unsol event is lost. I've not observed
> > >>>> any unsol event lost till now.
> > >>>>
> > >>>> As for the timeout, I suggest you use the codec->bus->workq instead of
> > >>>> creating a new workq. I think that will also give us some serialisation, i e,
> > >>>> protection against race conditions if the timeout happen at the same time as
> > >>>> the unsol event.
> > >>>
> > >>> Hi David,
> > >>>
> > >>> The new added "resume_wq" for hdmi codec is a wait queue, not a work queue like codec->bus->workq.
> > >>> It's expected to wake up as soon as the unsol event is got.
> > >>
> > >> Sure; but I don't see why you need a wait queue for that? Why don't you
> > >> just call the resume path from the unsol event handler
> > >> (hdmi_present_sense, or its caller), and then also cancel the timeout
> > >> handler (which can then be in the normal workq)?
> > >
> > > Because the delayed resume actually fakes as if the resume is done.
> > > This is necessary not to block other device's resume operation.
> > >
> > > Since it looks as if ready, user-space might restart things soon again
> > > before the delayed resume is really finished.  So, some serialization
> > > is required there.
> > 
> > Lin, would it be possible to add some chain of events description to the 
> > bug commit? The different contexts are just boggling my mind :-)
> 
> Yeah, a nice code flow picture would be helpful :)
> 
> > Assume we have two cases, system idle after S3 and immediate playback 
> > after S3.
> > 
> > Is this correct:
> > 
> > System idle:
> >   1. System skips hda_call_codec_resume and sets codec->resume_delayed.
> >   2. Since the codec is not reinitialized, nothing powers up the codec, 
> > so this is all that happens.
> >   3. Since unsol events are not enabled (?), we have a bug that jack 
> > detection does not work and cannot be detected from userspace...?
> > 
> > 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.
> 
> 
> Takashi
> 
> ---
> diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
> index 67e11ba..d0eafee 100644
> --- a/sound/pci/hda/patch_hdmi.c
> +++ b/sound/pci/hda/patch_hdmi.c
> @@ -1740,6 +1740,9 @@ static int generic_hdmi_init(struct hda_codec *codec)
>  		hdmi_init_pin(codec, pin_nid);
>  		snd_hda_jack_detect_enable(codec, pin_nid, pin_nid);
>  	}
> +
> +	spec->ready_to_resume = 0;
> +

Here needs #ifdef CONFIG_PM, obviously...


Takashi

>  	return 0;
>  }
>  
> @@ -1876,8 +1879,6 @@ static void intel_haswell_wait_ready_to_resume(struct hda_codec *codec)
>  	struct hdmi_spec *spec = codec->spec;
>  	int pin_idx;
>  
> -	spec->ready_to_resume = 0;
> -
>  	for (pin_idx = 0; pin_idx < spec->num_pins; pin_idx++) {
>  		struct hdmi_spec_per_pin *per_pin;
>  		hda_nid_t pin_nid;
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