Re: [PATCH] sound: usb: pcm: fix incorrect power state when playing sound after PM_AUTO suspend

[Takashi Iwai]

On Wed, 03 Jun 2020 05:05:15 +0200,
Macpaul Lin wrote:
> 
> On Tue, 2020-06-02 at 14:46 +0200, Takashi Iwai wrote:
> > On Tue, 02 Jun 2020 13:53:41 +0200,
> > Macpaul Lin wrote:
> > > 
> > > This patch fix incorrect power state changed by usb_audio_suspend()
> > > when CONFIG_PM is enabled.
> > > 
> > > After receiving suspend PM message with auto flag, usb_audio_suspend()
> > > change card's power state to SNDRV_CTL_POWER_D3hot. Only when the other
> > > resume PM message with auto flag can change power state to
> > > SNDRV_CTL_POWER_D0 in __usb_audio_resume().
> > > 
> > > However, when system is not under auto suspend, resume PM message with
> > > auto flag might not be able to receive on time which cause the power
> > > state was incorrect. At this time, if a player starts to play sound,
> > > will cause snd_usb_pcm_open() to access the card and setup_hw_info() will
> > > resume the card.
> > > 
> > > But even the card is back to work and all function normal, the power
> > > state is still in SNDRV_CTL_POWER_D3hot.
> > 
> > Hm, in exactly which situation does this happen?  I still don't get
> > it.  Could you elaborate how to trigger this?
> 
> I'm not sure if this will happen on laptop or on PC.
> We've found this issue on Android phone (I'm not sure if each Android
> phone can reproduce this.).
> 
> After booting the android phone, insert type-c headset without charging
> and play music at any duration, say, 1 second, then stop. Put phone away
> to idle about 17~18 minutes. Wait auto pm happened and the power state
> change to SNDRV_CTL_POWER_D3hot in sound/usb/card.c. Then wake up the
> phone, play music again. Then you'll probably found the music was not
> playing and the progress bar keep at the same position. It only happen 
> when power state is SNDRV_CTL_POWER_D3hot. If not (the power state is
> SNDRV_CTL_POWER_D0), repeat the steps for several times, then it will be
> produced at some time.
> 
> When it happened, sound_usb_pcm_open() will wake up the sound card by 
> setup_hw_info()->__usb_audio_resume(). However, the card and the
> interface is function properly right now, the power state keeps remain
> SNDRV_CTL_POWER_D3hot.

And at this point it's already something wrong.  We need to check why
SNDRV_CTL_POWER_D3hot is kept there, instead of working around the
rest behavior.

> The suggestive parameter settings from upper
> sound request will be pending since later snd_power_wait() call will
> still wait the card awaken. Ideally, auto PM should be recovered by
> sound card itself. But once the card is awaken at this circumstance, it
> looks like there are not more auto pm event. And the sound system of
> this interface will stuck here forever until user plug out the headset
> (reset the hardware).
> 
> The root cause is that once the card has been resumed, it should inform
> auto pm change the state back into SNDRV_CTL_POWER_D0 and mark the
> device is using by some one.
> 
> > > Which cause the infinite loop
> > > happened in snd_power_wait() to check the power state. Thus the
> > > successive setting ioctl cannot be passed to card.
> > > 
> > > Hence we suggest to change power state to SNDRV_CTL_POWER_D0 when card
> > > has been resumed successfully.
> > 
> > This doesn't look like a right solution for the problem, sorry.
> > The card PM status must be recovered to D0 when the autoresume
> > succeeds.  If not, something is broken there, and it must be fixed
> > instead of fiddling the status flag externally.
> 
> Yes, I agreed, but after checking the code in sound drivers, 
> it looks like there is only chance that auto pm triggered by low-level
> code in sound/usb/card.c. In kernel 4.14, auto pm suspend is triggered
> by snd_pcm_suspend_all(). In later kernel, it is triggered by
> snd_usb_pcm_suspend(). However, it looks like there are no any resume
> trigger to recover auto pm state when the card has been waken by
> sound_usb_pcm_open().

If a running PCM stream has been suspended, the stream needs to be
resumed manually by user-space.  There is no automatic resume.  You
can forget about it and skip scratching that surface.

Again, the point to be checked is why D3hot is kept after
snd_usb_autoresume() is called.

It's Android, and I wonder whether the system does the system-suspend
(S3), or it's all runtime PM?  Basically D3hot is set only for the
former, the system suspend, where the driver's PM callback is called
with PMSG_SUSPEND.  Please check this at first.  That is,
usb_audio_suspend() receives PMSG_SUSPEND or such, which makes
chip->autosuspended=1.  The D3hot flag is set only in this condition.

Then, check the resume patterns.  The usb-audio suspend/resume has
multiple refcounts.  One is the Linux device PM refcount, and
chip->active refcount, and chip->num_suspended_intf refcount.

The first one (PM refount) is the primary refcount to manage the whole
system, and this is incremented / decremented by the standard PM
calls.  The second one, chip->active, is a temporary flag to avoid the
re-entrance of the PM callbacks, and incremented at the probe enter
and __usb_audio_resume(), and decremented at the probe exit and
__usb_audio_resume() exist.  The last one, chip->num_suspended_intf is
a refcount for the multiple interfaces assigned to a single card.

And, the most suspicious case is the last one,
chip->num_suspended-intf.  It means that the device has multiple
USB interfaces and they went to suspend, while the resume isn't
performed for the all suspended interfaces in return.

If that's the case, you need to check where the suspend gets called to
which USB-interface (and which pm_message_t) and whether the resume
gets called for those.


thanks,

Takashi