Passing audio info from HDMI EDID beside speaker allocation

Passing audio info from HDMI EDID beside speaker allocation

[Patrick Lai]

Hi Takashi,

You proposed snd_pcm_query_chmaps() to query underlying hardware
speaker allocation. Please correct me if I have wrong understanding of
this API. On the other hand, HDMI EDID contains audio data other than
speaker allocation such as audio formats(LPCM, AC3, and etc). How are
these information other than speaker allocation passed back to the
user-space? Are there a standard kernel and alsa query interfaces now?

Thanks
Patrick

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Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: Passing audio info from HDMI EDID beside speaker allocation

[Patrick Lai]

On 10/4/2012 11:50 PM, Patrick Lai wrote:
> Hi Takashi,
>
> You proposed snd_pcm_query_chmaps() to query underlying hardware
> speaker allocation. Please correct me if I have wrong understanding of
> this API. On the other hand, HDMI EDID contains audio data other than
> speaker allocation such as audio formats(LPCM, AC3, and etc). How are
> these information other than speaker allocation passed back to the
> user-space? Are there a standard kernel and alsa query interfaces now?
>
> Thanks
> Patrick
>

Does anyone else have feedback for my query to Takashi?

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: Passing audio info from HDMI EDID beside speaker allocation

[Takashi Iwai]

At Thu, 04 Oct 2012 23:50:20 -0700,
Patrick Lai wrote:
> 
> Hi Takashi,
> 
> You proposed snd_pcm_query_chmaps() to query underlying hardware
> speaker allocation. Please correct me if I have wrong understanding of
> this API. On the other hand, HDMI EDID contains audio data other than
> speaker allocation such as audio formats(LPCM, AC3, and etc). How are
> these information other than speaker allocation passed back to the
> user-space? Are there a standard kernel and alsa query interfaces now?

In the case of HD-audio, it's passed via the normal IEC958 status bits
controls separately.  ELD itself is exposed as a byte array in a
control element, but it's read-only.


Takashi

Re: Passing audio info from HDMI EDID beside speaker allocation

[Patrick Lai]

On 10/8/2012 1:20 AM, Takashi Iwai wrote:

> In the case of HD-audio, it's passed via the normal IEC958 status bits
> controls separately.  ELD itself is exposed as a byte array in a
> control element, but it's read-only.

Thanks for the reply. Couple more questions

1. Is kcontrol "ELD" being read directly by application or there is
ALSA library API to parse the information.

2. Also, I see you submit this patch [PATCH 3/3] ELD proc interface for
HDMI sinks in 2008. I presume it's just for information purpose. You
still expect application to query for HDMI sink capability through
"ELD" kcontrol. Am I correct?

>
>
> Takashi
>


-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: Passing audio info from HDMI EDID beside speaker allocation

[Takashi Iwai]

At Mon, 22 Oct 2012 11:00:02 -0700,
Patrick Lai wrote:
> 
> On 10/8/2012 1:20 AM, Takashi Iwai wrote:
> 
> > In the case of HD-audio, it's passed via the normal IEC958 status bits
> > controls separately.  ELD itself is exposed as a byte array in a
> > control element, but it's read-only.
> 
> Thanks for the reply. Couple more questions
> 
> 1. Is kcontrol "ELD" being read directly by application or there is
> ALSA library API to parse the information.

Nothing so far.  It's just a raw data.

> 2. Also, I see you submit this patch [PATCH 3/3] ELD proc interface for
> HDMI sinks in 2008. I presume it's just for information purpose. You
> still expect application to query for HDMI sink capability through
> "ELD" kcontrol. Am I correct?

It's not prohibited for apps to parse the proc interface but it's not
guaranteed to be stable :)  So yes, parsing ELD manually would be a
safer way.


Takashi

Re: Passing audio info from HDMI EDID beside speaker allocation

[Pierre-Louis Bossart]

>>> In the case of HD-audio, it's passed via the normal IEC958 status bits
>>> controls separately.  ELD itself is exposed as a byte array in a
>>> control element, but it's read-only.
>>
>> Thanks for the reply. Couple more questions
>>
>> 1. Is kcontrol "ELD" being read directly by application or there is
>> ALSA library API to parse the information.
>
> Nothing so far.  It's just a raw data.
>
>> 2. Also, I see you submit this patch [PATCH 3/3] ELD proc interface for
>> HDMI sinks in 2008. I presume it's just for information purpose. You
>> still expect application to query for HDMI sink capability through
>> "ELD" kcontrol. Am I correct?
>
> It's not prohibited for apps to parse the proc interface but it's not
> guaranteed to be stable :)  So yes, parsing ELD manually would be a
> safer way.

I wrote some code to parse the ELD kcontrol to enable passthrough if AC3 
is supported by the receiver, I believe it's been integrated by Arun in 
a branch of PulseAudio. It's probably 1 year old now..