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

16 Mar 2016


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-----Original Message-----
From: Takashi Iwai [mailto:tiwai@suse.de]
Sent: Wednesday, March 16, 2016 10:28 PM
To: Yang, Libin
Cc: libin.yang@linux.intel.com; alsa-devel@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 15:24:54 +0100,
Yang, Libin wrote:
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-----Original Message-----
From: Takashi Iwai [mailto:tiwai@suse.de]
Sent: Wednesday, March 16, 2016 10:03 PM
To: Yang, Libin
Cc: libin.yang@linux.intel.com; alsa-devel@alsa-project.org; Lin,
Mengdong
Subject: Re: [alsa-devel] [PATCH] ALSA: hda - codec add DP MST
support
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for connection list
On Wed, 16 Mar 2016 14:53:09 +0100,
Yang, Libin wrote:
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From: Takashi Iwai [mailto:tiwai@suse.de]
Sent: Wednesday, March 16, 2016 3:56 PM
To: Yang, Libin
Cc: libin.yang@linux.intel.com; alsa-devel@alsa-project.org; Lin,
Mengdong
Subject: Re: [alsa-devel] [PATCH] ALSA: hda - codec add DP MST
support
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for connection list
On Wed, 16 Mar 2016 08:48:58 +0100,
Yang, Libin wrote:
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Hi Takashi,
> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai@suse.de]
> Sent: Wednesday, March 16, 2016 3:35 PM
> To: libin.yang@linux.intel.com
> Cc: alsa-devel@alsa-project.org; Yang, Libin; Lin, Mengdong
> Subject: Re: [alsa-devel] [PATCH] ALSA: hda - codec add DP
MST
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support
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> for connection list
>
> On Wed, 16 Mar 2016 02:47:31 +0100,
> libin.yang@linux.intel.com wrote:
> >
> > From: Libin Yang libin.yang@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@linux.intel.com
>
> The merge window was already opened, so it's too late for this
kind of
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> change for 4.6, in anyway.
That's OK. We can wait for later version. What do you think put
this
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patch
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and my later patches for MST in the topic branch, such as hdmi-
jack
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brach
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like before. Later patches for MST needs gfx driver support and
our
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gfx driver is not ready for it.
>
> But, the fundamental question: why do we need to manage
the
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cached
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> list of the widget connection with a device index?  In other
words,
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if
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> you have a different device index, does the widget connection
itself
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> also change?
Based on my test, it should be the same. But from the spec, it
says:
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7.3.3.42 Device Select
For Digital Display Pin Widget that is multi stream capable, the
Device
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Select control determines which
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Device Entry is currently selected and accessible by the Pin
Widget
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verbs
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which are controlling the sink
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device operations. This control verb is only required if it is a
Digital
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Display Pin Widget and multi stream
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capable.
The index is in relation to the Device List associated with the
widget.
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The
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index is a zero-based offset
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into the Device List. Once the Device Entry is selected by the Set
index,
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all subsequent Pin Widget verbs
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controlling the sink device operations will be directed to the
selected
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Device Entry, until the Device Select
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verb get updated with a new value. These Pin Widget verbs
include:
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  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 :)
We should take care of it :)
Regards,
Libin
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Takashi