[alsa-devel] [PATCH] ASoC: Intel: Power down links before turning off display audio power

Takashi Iwai tiwai at suse.de
Wed Jun 27 13:24:48 CEST 2018 

On Wed, 27 Jun 2018 12:57:22 +0200,
Sriram Periyasamy wrote:
> 
> On Wed, Jun 27, 2018 at 11:34:28AM +0200, Takashi Iwai wrote:
> > On Wed, 27 Jun 2018 11:17:55 +0200,
> > Sriram Periyasamy wrote:
> > > 
> > > On Wed, Jun 27, 2018 at 10:48:05AM +0200, Takashi Iwai wrote:
> > > > On Wed, 27 Jun 2018 10:35:35 +0200,
> > > > Sriram Periyasamy wrote:
> > > > > 
> > > > > On Tue, Jun 26, 2018 at 01:33:36PM +0200, Takashi Iwai wrote:
> > > > > > On Tue, 26 Jun 2018 13:24:01 +0200,
> > > > > > Sriram Periyasamy wrote:
> > > > > > > 
> > > > > > > On Mon, Jun 25, 2018 at 05:18:27PM +0200, Takashi Iwai wrote:
> > > > > > > > On Mon, 25 Jun 2018 16:51:12 +0200,
> > > > > > > > Sriram Periyasamy wrote:
> > > > > > > > > 
> > > > > > > > > On Mon, Jun 25, 2018 at 11:53:59AM +0200, Takashi Iwai wrote:
> > > > > > > > > > On Mon, 25 Jun 2018 11:23:17 +0200,
> > > > > > > > > > Sriram Periyasamy wrote:
> > > > > > > > > > > 
> > > > > > > > > > > On Mon, Jun 25, 2018 at 11:08:13AM +0200, Takashi Iwai wrote:
> > > > > > > > > > > > On Mon, 25 Jun 2018 10:53:49 +0200,
> > > > > > > > > > > > Sriram Periyasamy wrote:
> > > > > > > > > > > > > 
> > > > > > > > > > > > > On Fri, Jun 22, 2018 at 07:14:50PM +0200, Takashi Iwai wrote:
> > > > > > > > > > > > > > On Fri, 22 Jun 2018 18:42:24 +0200,
> > > > > > > > > > > > > > Pierre-Louis Bossart wrote:
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > On 6/22/18 4:25 AM, Sriram Periyasamy wrote:
> > > > > > > > > > > > > > > > On certain platforms, Display HDMI HDA codec was not going to sleep state
> > > > > > > > > > > > > > > > after the use when links are powered down after turning off the display
> > > > > > > > > > > > > > > > power. As per the HW recommendation, links are powered down before turning
> > > > > > > > > > > > > > > > off the display power to ensure that the codec goes to sleep state.
> > > > > > > > > > > > > > > 
> > > > > > > > > > > > > > > The change looks ok, I am still not clear on display power
> > > > > > > > > > > > > > > management. snd_hdac_display_power is called both from hdac_hdmi.c and
> > > > > > > > > > > > > > > skl.c in the respective probe/suspend/resume routines, wondering if
> > > > > > > > > > > > > > > this is redundant or intentional.
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > > Yeah, it looks like that skl.c keeps the display power on by assuming
> > > > > > > > > > > > > > that it's turned off by the codec driver, but it doesn't happen
> > > > > > > > > > > > > > actually.  I also find it fishy there...
> > > > > > > > > > > > > > 
> > > > > > > > > > > > > 
> > > > > > > > > > > > > snd_hdac_display_power is called intentionally to ensure that the codec is
> > > > > > > > > > > > > powered up before any communication is initiated from either skl.c or
> > > > > > > > > > > > > hdac_hdmi.c.
> > > > > > > > > > > > 
> > > > > > > > > > > > But who turns it down if the device is not used?
> > > > > > > > > > > 
> > > > > > > > > > > Powering down of codec is taken care in codec's suspend routine.
> > > > > > > > > > 
> > > > > > > > > > But you'll power up twice, no?  Once in skl_resume() (which is no
> > > > > > > > > > runtime resume but only for S3/S4) and once in codec resume.
> > > > > > > > > > I wonder who will turn down when you wake up from S3.
> > > > > > > > > 
> > > > > > > > > No. When entering to S3, hdmi_codec_prepare() will invoke the runtime
> > > > > > > > > resume of codec hdac_hdmi_runtime_resume() which power up the codec and
> > > > > > > > > skl_suspend power down the codec. When it wakes up from S3, skl_resume()
> > > > > > > > > powers up the codec and hdmi_codec_complete invokes the runtime suspend of
> > > > > > > > > codec hdac_hdmi_runtime_suspend() which powers down the codec.
> > > > > > > > 
> > > > > > > > Hm, but what about the i915 power well refcount, not the codec runtime
> > > > > > > > PM refcount?  Does the refcount reach to zero when the system goes to
> > > > > > > > runtime suspend?  That puzzles me.
> > > > > > > > 
> > > > > > > 
> > > > > > > Yes, i915 power well refcount goes to zero when system goes to runtime
> > > > > > > suspend. The value of bus->i915_power_refcount in snd_hdac_display_power
> > > > > > > is zero.
> > > > > > > 
> > > > > > > > > This design is required to achieve the runtime power reference count for
> > > > > > > > > codec device when it is put to S3/S4 while playback was going on.
> > > > > > > > 
> > > > > > > > ... and this "design" picture is completely missing.
> > > > > > > > That's why illustrating it was requested instead of a patch :)
> > > > > > > > 
> > > > > > > > > >  The runtime
> > > > > > > > > > suspend doesn't call snd_hdac_display_power() in skl.c.
> > > > > > > > > > 
> > > > > > > > > 
> > > > > > > > > Display power management for all runtime uses cases are handled in the
> > > > > > > > > codec driver hdac_hdmi.c.
> > > > > > > > 
> > > > > > > > But it means that hdac_hdmi.c does manage the extra decrement the
> > > > > > > > refcount that was taken in skl.c?
> > > > > > > >
> > > > > > > 
> > > > > > > No, snd_hdac_display_power is invoked in skl.c for the following cases,
> > > > > > > 
> > > > > > > skl_probe_work - display power on, enumurate the codec and display power
> > > > > > >                  off
> > > > > > > skl_suspend & skl_resume - display power off/on for S3/S0 cycle 
> > > > > > > 	                   respectively
> > > > > > > 
> > > > > > > snd_hdac_display_power is invoked in hdac_hdmi.c for the following cases,
> > > > > > > 
> > > > > > > hdac_hdmi_dev_probe - display power on, probe the device and put the
> > > > > > > 		      device to runtime suspend explicitly
> > > > > > > 
> > > > > > > runtime suspend & resume - display power off and on respectively
> > > > > > 
> > > > > > That puzzled me.  How does display refcount goes to zero at runtime
> > > > > > suspend of skl?  skl_suspend() is only for S3, not for runtime PM.
> > > > > > 
> > > > > 
> > > > > Runtime suspend and resume of skylake doesn’t perform reference counting
> > > > > of display. For an HDMI playback stream, below is the sequence.
> > > > > 
> > > > > Open:
> > > > > 1. skylake runtime resume
> > > > > 2. hdac_hdmi runtime resume --> ref count is incremented
> > > > > 
> > > > > Close:
> > > > > 1. hdac_hdmi runtime suspend --> ref count is decremented
> > > > > 2. skylake runtime suspend
> > > > > 
> > > > > > Suppose you probe skl, hdac_hdmi, then do runtime suspend hdac_hdmi
> > > > > > and skl respectively.  How does the display pm refcount go to zero?
> > > > > >
> > > > > 
> > > > > In skylake probe, the display ref count is incremented at start of probe
> > > > > and decremented at end of probe. The ref count decrement is not
> > > > > performed in skylake runtime suspend. In hdac_hdmi probe, the display
> > > > > refcount is incremented in probe, and decremented in hdac_hdmi runtime
> > > > > suspend.
> > > > 
> > > > Well, the display refcount is incremented in S3 resume in skl.c.
> > > > Who decrements it at runtime suspend?
> > > >
> > > 
> > > It is decremented at runtime suspend of codec hdac_hdmi_runtime_suspend().
> > > Below are sequence,
> > > 
> > > S3 cycle without playback going on,
> > > 
> > > Entering S3,
> > > 
> > > 1. hdmi_codec_prepare() invoke the runtime resume of codec
> > > 2. hdac_hdmi_runtime_resume() --> increments the refcount 
> > > 3. skl_suspend() -- > decrements the refcount
> > > 
> > > Wake up from S3,
> > > 
> > > 1. skl_resume() --> increments the refcount 
> > > 2. hdmi_codec_complete() invokes the runtime suspend of codec 
> > > 3. hdac_hdmi_runtime_suspend() -- > decrements the refcount
> > 
> > So you're calling the runtime suspend even though it's not runtime
> > resumed?  That confuses readers and needs a clear explanation
> > somewhere in the code.
> >
> 
> Yes, we will add a separate patch for this.

That'd be helpful.

> > And what's the case if multiple codecs are present?
> >
> 
> We need to check on multiple codecs scenario. Do you think any issues
> upfront?

No, and maybe my question was moot - it's only a single GPU, so always
a single codec, supposedly.


Takashi

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