From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: "Lu, Brent" <brent.lu@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 08:06:35 -0500 [thread overview]
Message-ID: <34604b9a-f479-3f92-7917-84f295a82fd8@linux.intel.com> (raw)
In-Reply-To: <CF33C36214C39B4496568E5578BE70C7402DBB9B@PGSMSX108.gar.corp.intel.com>
On 9/12/19 1:00 AM, Lu, Brent wrote:
>>>
>>> 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 design limitation is already handled by the fact that the SSP
operates in 2ch mode, so it's a different case from KBL where indeed the
DMIC-based back-end can support 4 channels.
>
> 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.
I get the error, I am just wondering if the fix is at the right
location. I'll look into it, give me until tomorrow.
next prev parent reply other threads:[~2019-09-12 13:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-06 1:24 [PATCH] ASoC: bdw-rt5677: channel constraint support 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
2019-09-12 13:06 ` Pierre-Louis Bossart [this message]
2019-09-27 12:34 ` Lu, Brent
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