Re: [PATCH v2] ALSA: HDA: Early Forbid of runtime PM

[Kai Vehmanen <kai.vehmanen@linux.intel.com>]

Hi,

On Fri, 28 Aug 2020, Kai Vehmanen wrote:

> On Fri, 28 Aug 2020, Takashi Iwai wrote:
> > Thanks.  The only concern is about the influence on the relevant ASoC
> > code, especially hdac_hda.c.
> > 
> > Kai, could you check whether this still works?
> 
> I did queue a SOF CI job for this v2 patch and I'm seeing some failures
> in module load/unload test that might be related and need checking before
> we merge:
> 
> https://sof-ci.01.org/linuxpr/PR2403/build4400/devicetest/

ok this took a bit longer than expected, but we've been debugging this 
with Emmanuel and found the rootcause.

So if we take this patch in and forbid runtime PM in device_new, it then 
becomes mandatory for all controllers to call set_default_power_save(). In 
SOF, this is only added recently to some machine drivers (notably the 
widely used generic HDA machine driver), which explains why tests pass on 
many targets. However, on platforms that use other machine drivers, 
set_default_power_save()/snd_hda_set_power_save() is not called, and 
device will never hit suspend (and this fails the tests).

To further complicate the matter, recently merged "ASoC: Intel: 
skl_hda_dsp_generic: Fix NULLptr dereference in autosuspend delay" will 
cause tests to fail on more platforms as HDMI/DP codec's powersave 
settings are not set.

The original patch is ok, but to merge it without a lot of regressions, 
we need to rework how powersave initial settings are done in SOF and other 
ASoC controllers using HDAC. I do think this is the right solution.

Br, Kai