Re: [PATCH] drm/i915/dp: DP audio API changes for MST

From: Takashi Iwai <tiwai@suse.de>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: libin.yang@linux.intel.com, intel-gfx@lists.freedesktop.org,
	alsa-devel@alsa-project.org,
	Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Subject: Re: [PATCH] drm/i915/dp: DP audio API changes for MST
Date: Thu, 04 Aug 2016 19:55:09 +0200	[thread overview]
Message-ID: <s5h8twcs9ky.wl-tiwai@suse.de> (raw)
In-Reply-To: <20160804173516.GK4329@intel.com>

On Thu, 04 Aug 2016 19:35:16 +0200,
Ville Syrjälä wrote:
> 
> On Thu, Aug 04, 2016 at 10:18:52AM -0700, Jim Bride wrote:
> > On Wed, Aug 03, 2016 at 10:08:12PM +0300, Ville Syrjälä wrote:
> > > On Tue, Aug 02, 2016 at 07:14:30PM -0700, Dhinakaran Pandiyan wrote:
> > > > DP MST provides the capability to send multiple video and audio streams via
> > > > one single port. This requires the API's between i915 and audio drivers to
> > > > distinguish between audio capable displays connected to a port. This patch
> > > > adds this support via an additional parameter 'int dev_id'. The existing
> > > > parameter 'port' does not change it's meaning.
> > > > 
> > > > dev_id =
> > > > 	MST	: pipe that the stream originates from
> > > > 	Non-MST	: -1
> > > > 
> > > > Affected APIs:
> > > > struct i915_audio_component_ops
> > > > -       int (*sync_audio_rate)(struct device *, int port, int rate);
> > > > +	int (*sync_audio_rate)(struct device *, int port, int dev_id,
> > > 
> > > Does the term 'dev_id' have some special meaning on the audio side? On
> > > the i915 side things would be less confusing if we just called it
> > > 'pipe'.
> > 
> > Yeah, it does.  All of the documentation on the audio side is written
> > in terms of device ID, so they asked for that nomenclature.
> 
> And is the device ID always the same as the pipe? Until now we've made
> due with passing the port instead of the pipe, so either the audio side
> didn't use the device ID, or its meaning changes based on how we drive
> things, or they dug it out from somewhere else based on the port?

This is my concern, too.  Currently we have a very wild assumption
even for the port mapping.  In the audio side, there is neither port
nor pipe.  There are only the widget node id and the device id.  The
former is supposedly corresponding to the port, and the latter to the
pipe.  But the audio side has absolutely no clue about how these are
connected.

Takashi
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