From mboxrd@z Thu Jan  1 00:00:00 1970
From: Russell King - ARM Linux <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
Subject: Re: [RFC v3 7/7] ASoC: hdmi-codec: Add ELD control
Date: Tue, 19 Jan 2016 17:14:33 +0000
Message-ID: <20160119171433.GQ19062@n2100.arm.linux.org.uk>
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To: Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>
Cc: Jean-Francois Moine <moinejf-GANU6spQydw@public.gmane.org>, alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org, Arnaud Pouliquen <arnaud.pouliquen-qxv4g6HH51o@public.gmane.org>, Koro Chen <koro.chen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>, Jyri Sarha <jsarha-l0cyMroinI0@public.gmane.org>, Liam Girdwood <lgirdwood-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>, Matthias Brugger <matthias.bgg-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Cawa Cheng <cawa.cheng-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
List-Id: alsa-devel@alsa-project.org

On Tue, Jan 19, 2016 at 02:47:50PM +0100, Lars-Peter Clausen wrote:
> On 01/12/2016 04:38 PM, Philipp Zabel wrote:
> > Exporting the ELD bytes to userspace allows an application to select
> > an appropriate audio format depending on the current capabilities of
> > the connected HDMI sink device.
> 
> This needs an explanation why this method, which will require explicit
> support in applications, should be used rather than the standard ALSA
> hardware capabilities reporting.

That can be summed up in one line:

ALSA doesn't know about all the different formats for compressed audio.

As far as I'm aware, applications today just lie to ALSA and use the
"16-bit PCM audio" formats (SNDRV_PCM_FORMAT_S16_LE or
SNDRV_PCM_FORMAT_U16_LE) to send compressed audio via ALSA, relying
on the IEC controls to set the channel status data correctly.

Maybe it would be nice to add formats for DTS, DTS-HD, AC3, OBA, etc
to the ALSA format list.

-- 
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