[alsa-devel] [PATCH V2] ASoC: fix hdmi codec driver contest in S3

[Takashi Iwai]

On Tue, 26 Mar 2019 12:02:13 +0100,
Yang, Libin wrote:
> 
> Hi Takashi,
> 
> >> >
> >> >On Tue, 26 Mar 2019 06:42:15 +0100,
> >> >Yang, Libin wrote:
> >> >(snip)
> >> >> Hi Takashi,
> >> >> Below is my draft patch, which doesn't work with
> >> >> pm_runtime_get_sync(). Is there anything wrong in my code?
> >> >(snip)
> >> >> And the dmesg is:
> >> >> [   36.087224] HDMI HDA Codec ehdaudio0D2: in hdmi_codec_resume
> >1890
> >> >ylb
> >> >> [   36.087230] HDMI HDA Codec ehdaudio0D2: in
> >> >hdac_hdmi_runtime_resume 2122 ylb 1
> >> >> [   36.087335] HDMI HDA Codec ehdaudio0D2: in
> >> >hdac_hdmi_cvt_output_widget_event 812 ylb
> >> >> [   40.097586] HDMI HDA Codec ehdaudio0D2: in
> >> >hdac_hdmi_runtime_resume 2135 ylb 2
> >> >> [   40.097766] HDMI HDA Codec ehdaudio0D2: in
> >> >hdac_hdmi_pin_output_widget_event 767 ylb
> >> >> [   45.108632] HDMI HDA Codec ehdaudio0D2: in
> >> >hdac_hdmi_pin_mux_widget_event 857 ylb
> >> >>
> >> >> >From the dmesg, hdac_hdmi_cvt_output_widget_event()
> >> >> is called between "ylb 1" and "ylb 2" in runtime_resume().
> >> >> This means xxx_event() registers setting runs before display power
> >> >> is turned on.
> >> >
> >> >OK, now I understood what went wrong.  It's a similar issue as we've
> >> >hit for the legacy HD-audio and figured out recently.
> >> >
> >> >If my understanding is correct, the problem is the call of
> >> >pm_runtime_force_resume() in PM resume callback combined with an
> >> >async work.  pm_runtime_force_resume() sets the runtime state
> >> >immediately to RPM_ACTIVE even before finishing the task.  The code
> >> >seems assuming blindly that there is no other conflicting task while
> >> >S3/S4 resume, but this is a problem.  That's why the next
> >> >pm_runtime_get_sync() wasn't blocked but just went through; since the
> >> >RPM flag was already set to RPM_ACTIVE in pm_runtime_force_resume(),
> >> >it thought as if it were already active, while the real runtime resume code
> >was still processing the callback.
> >>
> >> Yes, exactly right. And I have checked dev->power.runtime_status, it's
> >> RPM_ACTIVE when xxx_event() calls pm_runtime_get_sync().
> >>
> >> >
> >> >In the case of legacy HD-audio, we "fixed" the problem by avoiding
> >> >the trigger of async work at resume, but let it be triggered from
> >> >runtime resume.  In ASoC case, however, it's no option.
> >> >
> >> >Maybe a possible solution in the sound driver side would be to move
> >> >from system suspend/resume to ASoC component suspend/resume.  The
> >> >runtime suspend/resume can be kept as is, and call
> >> >pm_runtime_force_suspend and resume from the component
> >suspend/resume
> >> >callbacks.  Since the component callbacks are certainly processed
> >> >before DAPM events, this should assure the order.
> >>
> >> I have worked out another patch. This patch decouples the xxx_event()
> >> and runtime suspend/resume. This means in whichever case, xxx_event()
> >> can make sure display power is in the correct status. What do you think?
> >> On the same time, I will try the component suspend/resume. My
> >> understanding is that snd_hdac_display_power() should be called either
> >> in runtime_suspend/ resume or in component suspend/resume.
> >
> >This might work around the particular case, yes.  However it still makes me
> >uneasy as the root cause isn't full covered -- the other part of runtime resume
> >might be still pending while executing the DAPM event.
> >
> >Now, considering the idea with device_link_add() again: I guess it's
> >snd_soc_resume() who kicks off the DAPM even work?  If so, and if
> >snd_soc_resume() gets called from the machine driver, we can assure the PM
> >order via device_link_add() so that the codec driver is resumed before the
> >machine driver.  Then at the time the deferred resume work is executed, the
> >codec is ready, so the display power is on.
> 
> Yes, snd_soc_resume() kicks off the DAPM event work. The
> device PM sequence is good. The root cause is when hdmi runtime_resume
> calls snd_hdac_display_power(), it may sleep. The flow is:
> 
> 1. HDMI runtime_resume runs
> 2. HDMI runtime_resume calls snd_hdac_display_power(), but display
> driver is also operating display power and the mutex_lock is hold. So
> HDMI runtime_resume sleeps.
> 3. the deferred work is scheduled and xxx_event() is called.
> 
> This is wrong. All these happen because of the mutex_lock is hold
> by display driver, which causes HDMI runtime_resume sleep.

Well, the mutex lock itself is OK, and it's designed to behave so.

As mentioned, the root cause is pm_runtime_force_resume() that sets
RPM_ACTIVE while a concurrent task is running.

OTOH, this can be seen indeed as a PM dependency between devices, and
if we set the order explicitly, the problem can be avoided, too.  Then
the runtime resume of codec finishes before snd_soc_resume() is called
from the machine driver resume.

Also, moving to component PM would solve the problem, too, since it
also assures finishing the codec resume before the schedule_work()
call in snd_soc_resume().


thanks,

Takashi