linux-kernel - Re: [PATCH] ALSA: hda: Balance runtime/system PM if direct-complete is disabled

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Date:   Tue, 19 Jan 2021 01:27:03 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Takashi Iwai <tiwai@...e.com>,
        "Kenneth R . Crudup" <kenny@...ix.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Harsha Priya <harshapriya.n@...el.com>,
        "moderated list:SOUND" <alsa-devel@...a-project.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda: Balance runtime/system PM if direct-complete
 is disabled

On Mon, Jan 18, 2021 at 9:21 PM Takashi Iwai <tiwai@...e.de> wrote:
>
> On Mon, 18 Jan 2021 14:09:36 +0100,
> Kai-Heng Feng wrote:
> >
> > HDA controller can't be runtime-suspended after commit 215a22ed31a1
> > ("ALSA: hda: Refactor codjc PM to use direct-complete optimization"),
> > which enables direct-complete for HDA codec.
> >
> > The HDA codec driver didn't expect direct-complete will be disabled
> > after it returns a positive value from prepare() callback. However,
> > there are some places that PM core can disable direct-complete. For
> > instance, system hibernation or when codec has subordinates like LEDs.
>
> Hmm.  This sounds rather like the approach using the direct-complete
> isn't well suited for the purpose? The increasing number of
> regression reports worries me.

Direct-complete works fine on HDA controller but so far not so on HDA codec.
I think the main reason is that the codec doesn't have the middle
layer to handle the detail, while HDA controller has PCI bus to deal
with them.

>
> > So if a device is prepared for direct-complete but PM core still calls
> > codec's suspend or freeze callback, resume the device to keep PM
> > operations balanced.
>
> I find the ping-pong of the resume/suspend there a bit odd.  It's no
> refcount management but it invokes the real resume there, which is
> involved with lots of operations.

Yes. I'll find a better approach to address this.

>
> Can we rather skip the hda_codec_suspend() call instead (while
> changing dev->power.power_state)?

Maybe we can revert the most of the commit, and just leave
hda_codec_pm_complete(), which is the most relevant part of the patch.
Let me test a bit and send a new patch. Let me know if you don't like
this approach.

A question a bit unrelated to the discussion - how does
snd_hdac_power_up_pm() work for concurrent resume?
It can work for recursive call, but what if there are concurrent
resume request, but pm_runtime_get_sync() is still running?
The second call may access the codec which hasn't completed resume.

Kai-Heng

>
>
> thanks,
>
> Takashi
>
> > Reported-by: Kenneth R. Crudup <kenny@...ix.com>
> > Fixes: 215a22ed31a1 ("ALSA: hda: Refactor codec PM to use direct-complete optimization")
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > ---
> >  sound/pci/hda/hda_codec.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/sound/pci/hda/hda_codec.c b/sound/pci/hda/hda_codec.c
> > index 687216e74526..0afbced979df 100644
> > --- a/sound/pci/hda/hda_codec.c
> > +++ b/sound/pci/hda/hda_codec.c
> > @@ -2997,6 +2997,9 @@ static void hda_codec_pm_complete(struct device *dev)
> >
> >  static int hda_codec_pm_suspend(struct device *dev)
> >  {
> > +     if (pm_runtime_status_suspended(dev))
> > +             pm_runtime_resume(dev);
> > +
> >       dev->power.power_state = PMSG_SUSPEND;
> >       return hda_codec_suspend(dev);
> >  }
> > @@ -3009,6 +3012,9 @@ static int hda_codec_pm_resume(struct device *dev)
> >
> >  static int hda_codec_pm_freeze(struct device *dev)
> >  {
> > +     if (pm_runtime_status_suspended(dev))
> > +             pm_runtime_resume(dev);
> > +
> >       dev->power.power_state = PMSG_FREEZE;
> >       return hda_codec_suspend(dev);
> >  }
> > --
> > 2.29.2
> >