[alsa-devel] [PATCH] ALSA: hda - codec add DP MST support for connection list

[Takashi Iwai]

On Wed, 16 Mar 2016 15:24:54 +0100,
Yang, Libin wrote:
> 
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai at suse.de]
> > Sent: Wednesday, March 16, 2016 10:03 PM
> > To: Yang, Libin
> > Cc: libin.yang at linux.intel.com; alsa-devel at alsa-project.org; Lin,
> > Mengdong
> > Subject: Re: [alsa-devel] [PATCH] ALSA: hda - codec add DP MST support
> > for connection list
> > 
> > On Wed, 16 Mar 2016 14:53:09 +0100,
> > Yang, Libin wrote:
> > >
> > >
> > > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > > Sent: Wednesday, March 16, 2016 3:56 PM
> > > > To: Yang, Libin
> > > > Cc: libin.yang at linux.intel.com; alsa-devel at alsa-project.org; Lin,
> > > > Mengdong
> > > > Subject: Re: [alsa-devel] [PATCH] ALSA: hda - codec add DP MST
> > support
> > > > for connection list
> > > >
> > > > On Wed, 16 Mar 2016 08:48:58 +0100,
> > > > Yang, Libin wrote:
> > > > >
> > > > > Hi Takashi,
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > > > > Sent: Wednesday, March 16, 2016 3:35 PM
> > > > > > To: libin.yang at linux.intel.com
> > > > > > Cc: alsa-devel at alsa-project.org; Yang, Libin; Lin, Mengdong
> > > > > > Subject: Re: [alsa-devel] [PATCH] ALSA: hda - codec add DP MST
> > > > support
> > > > > > for connection list
> > > > > >
> > > > > > On Wed, 16 Mar 2016 02:47:31 +0100,
> > > > > > libin.yang at linux.intel.com wrote:
> > > > > > >
> > > > > > > From: Libin Yang <libin.yang at linux.intel.com>
> > > > > > >
> > > > > > > This patches adds the support of connection list for DP MST.
> > > > > > > With this, hdmi driver in DP MST mode can easily reuse
> > > > > > > the connection list mechanism.
> > > > > > >
> > > > > > > Signed-off-by: Libin Yang <libin.yang at linux.intel.com>
> > > > > >
> > > > > > The merge window was already opened, so it's too late for this
> > kind of
> > > > > > change for 4.6, in anyway.
> > > > >
> > > > > That's OK. We can wait for later version. What do you think put this
> > > > patch
> > > > > and my later patches for MST in the topic branch, such as hdmi-jack
> > > > brach
> > > > > like before. Later patches for MST needs gfx driver support and our
> > > > > gfx driver is not ready for it.
> > > > >
> > > > > >
> > > > > > But, the fundamental question: why do we need to manage the
> > > > cached
> > > > > > list of the widget connection with a device index?  In other words,
> > if
> > > > > > you have a different device index, does the widget connection
> > itself
> > > > > > also change?
> > > > >
> > > > > Based on my test, it should be the same. But from the spec, it says:
> > > > >
> > > > > 7.3.3.42 Device Select
> > > > > For Digital Display Pin Widget that is multi stream capable, the
> > Device
> > > > Select control determines which
> > > > > Device Entry is currently selected and accessible by the Pin Widget
> > verbs
> > > > which are controlling the sink
> > > > > device operations. This control verb is only required if it is a Digital
> > > > Display Pin Widget and multi stream
> > > > > capable.
> > > > > The index is in relation to the Device List associated with the widget.
> > The
> > > > index is a zero-based offset
> > > > > into the Device List. Once the Device Entry is selected by the Set
> > index,
> > > > all subsequent Pin Widget verbs
> > > > > controlling the sink device operations will be directed to the selected
> > > > Device Entry, until the Device Select
> > > > > verb get updated with a new value. These Pin Widget verbs include:
> > > > >   Connection Select
> > > > >   Get Connection List Entry
> > > > >   Amplifier Gain/Mute
> > > > >   Power State
> > > > >   Pin Widget Control
> > > > >   ELD Data
> > > > >   DIP-Size
> > > > >   DIP-Index
> > > > >   DIP-Data
> > > > >   DIP-XmitCtrl
> > > > >   Content Protection Control
> > > > >   ASP Channel Mapping
> > > > >
> > > > > So my understand is this may be changed.
> > > >
> > > > But the pin widget is the terminal.  So, if you have a device index to
> > > > choose a device there, the widget connection list itself doesn't
> > > > change.  Or am I missing anything?
> > >
> > > The pin may connect to several converters (for example), and it
> > > can choose which converter to use. And from the spec, it seems
> > > each device entry can have different connection list entry.
> > > However from my test, all device entries on the same pin will have
> > > the same list.
> > 
> > Hrm, OK, so it makes sense to keep the list.  OTOH, it means that the
> > connection list may change endlessly depending on the device index.
> > And, we likely need to clean up the connection list at unplug.
> 
> I'm not sure whether the connection list will be changed when unplug.
> Suppose it should be the capability and will not change?

How can we know?  Hardware designers have often a too creative mind :)


Takashi