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

[Arun Raghavan]

+pulseaudio-discuss for information

On Wed, 24 Jun 2020, at 1:33 PM, Takashi Iwai wrote:
> On Wed, 24 Jun 2020 19:05:14 +0200,
> Pierre-Louis Bossart wrote:
> > 
> > 
> > 
> > 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.
> 
> I guess we can check it from the codec ID?  Change the probe function
> for Skylake+ codecs to patch_i915_skl_hdmi and co, and set the flag
> there.
> 
> > >> 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
> 
> Yes, it's been the primary knob for years to turn on/off the runtime
> PM for HD-audio and other legacy drivers.  This was used by powertop
> or some other power-aware daemons and tools, to be toggled dynamically
> per the power cable state or such.
> 
> And, how the silent stream feature should be seen?
> Should it be a system-wide root-only setup or adjustable per user?
> Would it be changed often?  Such questions and answers will lead us to
> the right direction, I hope.

For audio, would UCM not be the appropriate point for a system integrator to decide how the audio device should be set up?

This would allow for a choice based on the situation in which the device is actually being deployed without users having to muck around with module parameters -- maybe someone wants want this enabled for an HTPC setup, but not on a desktop connected to a monitor.

-- Arun