linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Lu, Brent" <brent.lu@intel.com>
To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
	"alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
Cc: "Rojewski, Cezary" <cezary.rojewski@intel.com>,
	"kuninori.morimoto.gx@renesas.com"
	<kuninori.morimoto.gx@renesas.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"yang.jie@linux.intel.com" <yang.jie@linux.intel.com>,
	"tiwai@suse.com" <tiwai@suse.com>,
	"liam.r.girdwood@linux.intel.com"
	<liam.r.girdwood@linux.intel.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Subject: RE: [alsa-devel] [PATCH] ASoC: bdw-rt5677: channel constraint support
Date: Thu, 12 Sep 2019 06:00:45 +0000	[thread overview]
Message-ID: <CF33C36214C39B4496568E5578BE70C7402DBB9B@PGSMSX108.gar.corp.intel.com> (raw)
In-Reply-To: <99769525-779a-59aa-96da-da96f8f09a8a@linux.intel.com>

> >
> > The story is Chrome has a tool called alsa_conformance_test which runs
> > capture or playback against a PCM port with all possible
> > configurations (channel, format, rate) then measure if the sample rate
> > is correct. Since the channel max number reported is 4, it tests the
> > 4-channel 48K capture and reports the actual sample rate is 24000
> > instead of 48000. That's the reason we want to add a constraint in
> > machine driver to avoid user space programs trying to do 4 channel
> recording since this machine does not support it in the beginning.
> 
> ok, that helps get context, thanks for the details.
> 
> I would have expected some error to be returned if there's a front-end
> opened with 4 channels and the back-end only supports two. Adding the
> constraint seems like a work-around to avoid dealing with the mismatch
> between FE and BE. I don't understand DPCM enough to suggest an
> alternative though. Ranjani, can you help on this one?
> 
> And even if we agree with this solution, it'd be nice to apply it for the
> Broadwell machine driver for consistency.

It's not only the mismatch but also the design limitation. According to the 
information from google, the board (samus) only uses two microphone so 
3 or 4 channel recording are not supported. That's the reason we leverage 
the constraint from other machine driver (like kbl_da7219_max98357a.c) 
to remove the 3 and 4 channel recording option.

The difference after the constraint is implemented is that the 
snd_pcm_hw_params_set_channels() function will return error (Invalid 
argument) when channel number is 3 or 4 so the application knows the 
configuration is not supported.


Regards,
Brent


  reply	other threads:[~2019-09-12  6:04 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-06  1:24 Brent Lu
2019-09-06 14:20 ` [alsa-devel] " Pierre-Louis Bossart
2019-09-09  6:34   ` Lu, Brent
2019-09-09 17:53     ` Pierre-Louis Bossart
2019-09-10  8:28       ` Lu, Brent
2019-09-10 14:12         ` Pierre-Louis Bossart
2019-09-12  6:00           ` Lu, Brent [this message]
2019-09-12 13:06             ` Pierre-Louis Bossart
2019-09-27 12:34               ` Lu, Brent

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CF33C36214C39B4496568E5578BE70C7402DBB9B@PGSMSX108.gar.corp.intel.com \
    --to=brent.lu@intel.com \
    --cc=alsa-devel@alsa-project.org \
    --cc=broonie@kernel.org \
    --cc=cezary.rojewski@intel.com \
    --cc=kuninori.morimoto.gx@renesas.com \
    --cc=liam.r.girdwood@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pierre-louis.bossart@linux.intel.com \
    --cc=ranjani.sridharan@linux.intel.com \
    --cc=tglx@linutronix.de \
    --cc=tiwai@suse.com \
    --cc=yang.jie@linux.intel.com \
    --subject='RE: [alsa-devel] [PATCH] ASoC: bdw-rt5677: channel constraint support' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).