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Subject: Re: [PATCH v2] ASoC: bdw-rt5650: remove 3-channel capture support
To:     "Lu, Brent" <brent.lu@intel.com>,
        "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
Cc:     Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>,
        "Rojewski, Cezary" <cezary.rojewski@intel.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Takashi Iwai <tiwai@suse.com>,
        Jie Yang <yang.jie@linux.intel.com>,
        Liam Girdwood <liam.r.girdwood@linux.intel.com>,
        Ben Zhang <benzh@chromium.org>,
        "Chiang, Mac" <mac.chiang@intel.com>,
        Mark Brown <broonie@kernel.org>
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From:   Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
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Date:   Tue, 14 Apr 2020 13:53:59 -0500
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On 4/13/20 9:29 AM, Lu, Brent wrote:
>>
>> That looks like an error caught by the ALSA conformance tool?
>>
>> What are the odds that we have a similar issue with the other broadwell
>> drivers which don't have a constraint on the number of channels either on
>> their 'System PCM' dailink?
>>
>> Thanks
>> -Pierre
>>
> 
> Yes. That's why I am sending patch for this old BDW platform...
> 
> So far as I know only 'buddy' supports 2/4-channel recording while other BDW
> Chrome products should support stereo recording only. Therefore, this defect
> should only be triggered by the ALSA conformance tool.
> 
> I am think about implementing the constraint in FE DAI's startup() callback
> instead of DAI Link's callback. Since the channels_max is 4 for the capture
> stream, ALSA conformance tool will always test 3-channel recording on any
> platforms using this driver. Does it make sense to you?

Looking back at previous threads, you indicated that the number of 
channels supported in propagated from BE to FE, so a similar patch to 
add 2ch constraints for bwd-rt5677 was dropped  ("ASoC: bdw-rt5677: 
channel constraint support")

Actually I am not sure it was dropped since later you submitted another 
patch ("ASoC: bdw-rt5677: enable runtime channel merge"), and my 
feedback was that it seemed simpler to add constraints on all machine 
drivers.

And now this patch only addresses bdw-rt5650.c but with the initial 
solution suggested for bdw-rt5677.c

It seems like a generic problem on all Broadwell devices so let's solve 
with one a single patchset.

Shouldn't we just add the 2ch constraints for broadwell.c and 
bdw-rt5677.c, and the 2 or 4ch constraint for bdw-rt5650.c? Would this 
work for you?

Thanks
-Pierre