[alsa-devel] [PATCH] ALSA: hda - Autosuspend controller after probe even if codecs are already suspended

[Takashi Iwai]

On Fri, 26 Feb 2016 18:39:57 +0100,
ville.syrjala at linux.intel.com wrote:
> 
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> azx_probe_continue() uses pm_runtime_put_noidle() to drop the rpm
> usage_count, which means that if it's the last reference the
> autosuspend of the controller won't actually happen. So if the codecs
> autosuspend before the azx_probe_continue() drops the last
> reference we'll fail to autosuspend the controller. This does happen
> in practice, but not every time. As can be seen in [1] the controller
> autosuspend attempt fails due to the usage_count when suspending the
> codecs. A bit later we see the the contoller usage_count dropping to
> zero without further attempts at autosuspend.
> 
> Fix the problem by using pm_runtime_put_autosuspend() instead, which
> will kick off the autosuspend of the controller even if the codecs
> are already asleep. As can be seen in [2] the controller autosuspend
> still fails while suspending the codecs, but later on we see another
> autosuspend attempt after dropping the usage_count to 0.
> 
> I was also a bit worried that there might still be a race between the
> controller autosuspend and the rest of the code in azx_probe_continue().
> So I also tried replacing the the put_noidle() with put_sync_suspend().
> No explosions occurred, so I'm somewhat satisfied that there are no
> serious problems in this area.

A good catch!

The change should be safe, as this is the point where already all
initialization has been done.

I queued it to for-next branch, since this is no super-urgent issue to
be fixed in 4.5.


thanks,

Takashi