From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH v5] drm/i915: pass ELD to HDMI/DP audio
 driver
Date: Sat, 12 Nov 2011 10:27:26 +0800
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To: Takashi Iwai <tiwai@suse.de>
Cc: "Wang, Zhenyu Z" <zhenyu.z.wang@intel.com>, "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>, "Barnes, Jesse" <jesse.barnes@intel.com>, Jeremy Bush <contractfrombelow@gmail.com>, Christopher White <c.white@pulseforce.com>, "Bossart,
	Pierre-louis" <pierre-louis.bossart@intel.com>
List-Id: intel-gfx@lists.freedesktop.org

(snip)
> > > > > And I'm not sure whether HDMI audio is played
> > > > > while DPMS is off.  I haven't tested it.
> > > > 
> > > > It will go silence on DPMS. I noticed this while doing long term HDMI
> > > > audio playback tests.  This should better be fixed in future on the
> > > > graphics side.
> > > 
> > > Hm, but I wonder what could be done alternatively.
> > > Hopefully there is a register for video-only control...
> > 
> > There may be some mode that can keep video off while still keep
> > minimal signals to play HDMI sound?
> 
> Let's hope :)

Looks very possible, here is the clue of hardware support:

        TRANS_DP_CTL - Transcoder DisplayPort Control

        bit 26: Transcoder DP Audio Only Mode

Thanks,
Fengguang