[alsa-devel] [RFC PATCH 0/2] ALSA: hda - DP MST audio for Jack support

[Yang, Libin]

> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Tuesday, December 22, 2015 5:00 PM
> To: Libin Yang
> Cc: Yang, Libin; mengdong.lin at linux.intel.com; alsa-devel at alsa-
> project.org
> Subject: Re: [alsa-devel] [RFC PATCH 0/2] ALSA: hda - DP MST audio for
> Jack support
> 
> On Tue, 22 Dec 2015 09:47:12 +0100,
> Libin Yang wrote:
> >
> > Hi Takashi,
> >
> > On 11/09/2015 11:15 PM, Takashi Iwai wrote:
> > > On Mon, 09 Nov 2015 16:00:01 +0100,
> > > Yang, Libin wrote:
> > >>
> > >> Hi Takashi,
> > >>
> > >>> -----Original Message-----
> > >>> From: Takashi Iwai [mailto:tiwai at suse.de]
> > >>> Sent: Monday, November 09, 2015 3:59 PM
> > >>> To: Libin Yang
> > >>> Cc: alsa-devel at alsa-project.org; mengdong.lin at linux.intel.com;
> Yang,
> > >>> Libin
> > >>> Subject: Re: [alsa-devel] [RFC PATCH 0/2] ALSA: hda - DP MST
> audio for
> > >>> Jack support
> > >>>
> > >>> On Wed, 04 Nov 2015 07:23:14 +0100,
> > >>> Libin Yang wrote:
> > >>>>
> > >>>>
> > >>>> On 11/04/2015 12:49 AM, Takashi Iwai wrote:
> > >>>>> On Tue, 03 Nov 2015 09:42:54 +0100,
> > >>>>> libin.yang at linux.intel.com wrote:
> > >>>>>>
> > >>>>>> From: Libin Yang <libin.yang at linux.intel.com>
> > >>>>>>
> > >>>>>> This is the patch set for Jack support for DP MST audio
> > >>>>>>
> > >>>>>> Libin Yang (2):
> > >>>>>>     ALSA: hda - jack support DP MST audio
> > >>>>>>     ALSA: hda - hdmi audio add dynamically jack binding to pin
> > >>>>>
> > >>>>> I'm somehow confused by this patch series.
> > >>>>> Is the unsolicited event handling itself changed for MST?  I mean,
> you
> > >>>>> cannot know which MST dev# is given beforehand, while you
> seem
> > >>> trying
> > >>>>> to assign such a number to the jack object.
> > >>>>
> > >>>> Oh, sorry I forgot to mention that we only operate on device
> entry 0
> > >>>> so far in the code. It's misleading.
> > >>>>
> > >>>> These patches don't operate on MST audio. The full MST audio
> driver
> > >>>> support will be implemented in the later patches. The patches help
> to
> > >>>> prepare supporting MST audio.
> > >>>>
> > >>>> The purpose of the patches is try to dynamically attach the Jack.
> > >>>
> > >>> Well, only judging from the quick glance, I don't buy this strategy,
> > >>> sorry.  Currently for HDMI/DP, the jack is for PCM, not for pin.
> > >>> Namely, user-space watches the jack notification to judge whether
> the
> > >>> corresponding PCM is available or not.  You're trying to change this
> > >>> scheme completely.
> > >>
> > >> The patch is to make sure the jack is bound to PCM statically.
> > >> This patch is needed because in old code,  it will create jack with:
> > >> for (pin_idx = 0; pin_idx < spec->num_pins; pin_idx++) {
> > >> 	...
> > >> 	err = generic_hdmi_build_jack(codec, pin_idx);
> > >> 	...
> > >> }
> > >> Which means the jack is created based on pin number and pin_idx.
> > >> As a pin is bound statically to the PCM, the jack is statically bound to
> PCM.
> > >
> > > OK, so far, so good.
> > >
> > >> Now we are using the dynamic pcm bound. If we use the old code to
> > >> create the jack, the jack will be bound to pin. So we need the patch,
> > >> which will use the new code:
> > >> for (pcm_idx = 0; pcm_idx < spec-> pcms_used; pcm_idx++) {
> > >> 	...
> > >> 	err = generic_hdmi_build_jack(codec, pcm_idx);
> > >> 	...
> > >> }
> > >> which makes sure that the jack is bound to PCM (jack[0] is bound
> > >> to pcm[0], jack[1] is bound to pcm[1] and so on).
> > >>
> > >> If there is no monitor, no pin is bound to the PCM.
> > >> So no pin is bound to the Jack. When there is a monitor connected,
> > >> the pin is bound to a proper PCM. So we should bind the PCM's jack
> > >> to the pin.
> > >>
> > >> For example, jack0 is bound to the PCM 3 (the first jack is bound
> > >> to the first PCM statically). When a monitor is connected to pin 5,
> > >> PCM 3 will be assigned to the pin. We need bind jack 0 to pin 5.
> > >> When monitor is disconnected, we must unbind the jack 0 from pin
> 5.
> > >> These operation are done in function
> > >> snd_hda_jack_bind/ snd_hda_jack_unbind.
> > >
> > > Then we shouldn't use the hda_jack.c code at all for HDMI/DP.
> > > For HDMI/DP with the dynamic PCM binding, the only state to check
> is
> > > its PCM assignment.  It doesn't have to issue the jack state check via
> > > HDA verb at all.  This should make things a lot easier.
> >
> > I'm now porting the jack supporting for MST audio. The code on
> > hdmi-jack branch will create jack differently based codec_has_acomp()
> > condition. Does this mean MST Jack binding will handle both situation?
> 
> Ideally, yes.
> 
> > My idea is:
> > 1. Add struct snd_jack *jack[] member in hdmi_spec.
> > 2. Create the jack based on PCM
> > 3. Assign spec->jack[i] to per_pin->acomp_jack when pin is connected.
> >
> > This should be OK for codec_has_acomp sitation.
> 
> Hrm, not really.  As already discussed, a jack is associated to each
> PCM, and notified plug/unplug when it's assigned / unassigned.
> That is, you don't have to keep extra jack array.  When a PCM is
> assigned or unassigned, simply notify per_pin->acomp_jack of that PCM.
> That's all.  So there shouldn't be too many difference from the
> current situation.

If so, the snd_jack is dynamically bound to PCM. This means
the jack is bound to the pin, and user space must get the pcm-pin
mapping to know the jack is bound to which PCM. Then it can decide
how to operate on the PCM. Not sure it is compatible with current
pulseaudio. 

> 
> > But what about the
> > other situation? The other situation still uses the hda_jack_tbl and
> > etc. So we still need handle hda jack if we want to reuse the current
> > code.
> 
> For other, it's similar.  The jack is associated with PCM, which is
> virtually bound with per_pin.  And when it's assigned / unassigned,
> call it with the given per_pin->pin_nid.
> 
> 
> Takashi