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. Takashi
