Re: [PATCH] ALSA: hda/hdmi: Add Intel silent stream support

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 6/24/20 11:43 AM, Takashi Iwai wrote:
> On Wed, 24 Jun 2020 17:33:45 +0200,
> Pierre-Louis Bossart wrote:
>>
>>
>>>>> The silent stream is enabled with a Kconfig option, as well as a kernel
>>>>> parameter should there be a need to override the build time default.
>>>>
>>>> I'm not sure whether the module option is the best interface.
>>>> An alternative is a mixer element that controls dynamically.  Then
>>>> it'll be per card unlike the module option.
>>>
>>> +1, kcontrol seems the appropriate way to control this.
>>
>> It was my suggestion to use Kconfig+kernel parameter for
>> simplicity/overrides.
>>
>> The kcontrol is a nice idea, but in practice we typically only have
>> one card dealing with HDMI.
> 
> Not really.  There are systems with two HDMI outputs from both
> integrated and discrete GPUs.  Most modern systems are only with
> hybrid graphics, though.

Ok, maybe I am mistaken, in most of the HDMI issues we've seen only one 
HDMI source.

But it's a good point that this is only supposed to be used for Intel 
whether it's a kernel parameter or a kcontrol shouldn't this be 
dependent on a PCI ID being detected and a SKYLAKE flag being set? it's 
my understanding that this applies from Skylake to TigerLake, not before.

>> It also doesn't have a UCM representation
>> so would force the use of amixer and manual configs, or the UCM file
>> would always set the mode.
> 
> But people usually use the distro kernels, so the situation is more or
> less equivalent; you'd have to adjust a module option manually if you
> want a different one from the default, and you'd have to be root to
> change it.
> 
> So, rather the question is how we should provide the setup of such
> parameter.  It's supposed to be a part of power management stuff that
> should be touched by either a smart PM tool or a manual override such
> as runtime PM setup?  Or can it be seen as a more casual tuning?

I am not aware of such tools. The only thing I know is that some of the 
HDaudio power settings are already controlled by kernel parameters, e.g.

/etc/modprobe.d/audio_powersave.conf
options snd_hda_intel power_save=1