[alsa-devel] [Intel-gfx] Need your advice: Add a new communication inteface between HD-Audio and Gfx drivers for hotplug notification/ELD update

[Lin, Mengdong]

> -----Original Message-----
> From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
> Sent: Wednesday, February 19, 2014 7:30 PM

> > > > Is there a 1:1 mapping between these connector nodes and ports of
> > > > Gfx
> > > display engine?
> > > > Eg. For Haswell Ultrabook, under
> > > > /sys/devices/pci0000:00/0000:00:02.0/drm/card0/
> > > > There are four connector nodes,
> > > > card0-DP-1		-> DDI port B
> > > > card0-eDP-1/		-> DDI port A
> > > > card0-HDMI-A-1/	-> DDI Port C
> > > > card0-HDMI-A-2/	-> Which DDI port ?  Haswell-ULT does not
> > > support port D, and I think port E is for VGA.
> > >
> > > There's no fixed mapping with the port and the connector name. The
> > > number in the connector name is basically just a running number per
> > > connector type. However I do believe we do register the connectors
> > > in the order of the ports more or less always, so you can
> > > *sometimes* deduce the port name from the connector.
> > >
> > > I suppose in this example HDMI-A-1 is port B, HDMI-A-2 is port C,
> > > and
> > > DP-1 can be either port B or port C. DP++ is the reason why we have
> > > overlapping DP and HDMI connectors for the same port.
> >
> > Thanks for clarification, Ville!
> >
> > Does Haswell support DP++ on port B/C/D?
> 
> Yes.
> 
> > And will the name of these connector node change after system boot,
> e.g. after S3/S4 cycles or hot-plug?
> 
> The connector names can't change, except if you unload+reload the driver.

It seems okay. We could let the gfx driver notify the audio driver when the connector nodes are destroyed or recreated.
And the audio driver can always know the connector names no matter they change or not.

> But I suppose DP MST might change this. Or maybe we'll just expose three
> new fixed DP connectors per DDI port. One for each potential stream.

It would be fine.

> > As long as the connector name is constant, it can help to find out the
> screen status no matter the port works in HDMI or DP mode.
> >
> > There is 1:1 mapping between audio output pins and DDI ports.
> 
> So I guess we need to expose the port->connector mapping somehow to
> the audio driver.

When the gfx driver enables audio, the mapping between transcoder/port/connector is established.
And the gfx driver can notify audio the connector name, to help the user space to know the audio could be output to which screen.

> How does this work with DP MST? On the display side the audio stuff
> happens in the transcoder, not the DDI port, AFAICS. For DP MST each
> transcoder can provide a single stream.

DP MST is not supported in the audio driver atm. But it could support in the future.
E.g. for Haswell, audio driver can know the device index of a monitor connected to a port through HW unsolicited event, 
when the gfx driver establishes mapping between a transcoder and a monitor and enables audio on the transcoder. 
Different monitors connected to a same port simultaneously have different device index. 
Then the audio driver will specify the device index for an audio stream that flows to the right transcoder. 
And we're planning to replace the HW unsolicited event notification by SW notification between the gfx and audio driver.

Thanks
Mengdong

> > And the new ALSA PCM 'screen' control for a pin can reflect the
> connector name in right mode. E.g. for pin/port B, it can return HDMI-A-1
> or DP-1 depending on what kind of monitor is connected.
> >
> > Thanks
> > Mengdong
> >
> > > >
> > > > Hi Takashi,
> > > >
> > > > To make user space figure out which audio output is connected to
> > > > which
> > > screen (connector), maybe we can define a new ALSA control for each
> > > HDMI/DP PCM device:
> > > > e.g. numid=x,iface=PCM,name='Screen',device=3
> > > > Reading the control will return the name of the DRM connector
> > > > nodes
> > > like ' card0-DP-1'. The audio driver can get the connector name from
> > > the gfx driver.
> > > >
> > > > For DP1.2 Multi-stream transport, it's not supported by i915 and
> > > > HD-A
> > > driver now. But probably there will be sub-nodes for the DP
> > > connector node in the future and an index in their name can be used
> > > distinguish monitors connected to the same DP port, like
> > > card0-DP-1.1, card0-DP-1.2,
> > > card0-DP-1.3 ... These names can be used by the above ALSA PCM
> 'Screen'
> > > control, so we can still know which audio output is to which monitor.
> > > >
> > > > Thanks
> > > > Mengdong
> > > >
> > > > _______________________________________________
> > > > Intel-gfx mailing list
> > > > Intel-gfx at lists.freedesktop.org
> > > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> > >
> > > --
> > > Ville Syrjälä
> > > Intel OTC
> 
> --
> Ville Syrjälä
> Intel OTC