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Subject: Re: [alsa-devel] [PATCH] ASoC: bdw-rt5677: enable runtime channel
 merge
To:     "Lu, Brent" <brent.lu@intel.com>,
        "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
Cc:     "Rojewski, Cezary" <cezary.rojewski@intel.com>,
        Liam Girdwood <liam.r.girdwood@linux.intel.com>,
        Jie Yang <yang.jie@linux.intel.com>,
        Mark Brown <broonie@kernel.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>,
        "Zavras, Alexios" <alexios.zavras@intel.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Message-ID: <63da3995-b807-f9e6-6f09-a90e6b8e8e53@linux.intel.com>
Date:   Mon, 21 Oct 2019 05:41:55 -0500
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>> In the DAI link "Capture PCM", the FE DAI "Capture Pin" supports 4-channel
>> capture but the BE DAI supports only 2-channel capture. To fix the channel
>> mismatch, we need to enable the runtime channel merge for this DAI link.
>>
> 
> Hi Pierre,
> 
> This patch is for the same issue discussed in the following thread:
> https://patchwork.kernel.org/patch/11134167/
> 
> We enable the runtime channel merge for the DMIC DAI instead of adding a
> machine driver constraint. It's working good on chrome's 3.14 branch (which
> requires some backport for the runtime channel merge feature). Please let
> me know if this implementation is correct for the FE/BE mismatch problem.

Sorry, I don't fully understand your points, and it's the first time I 
see anyone use this .dpcm_merged_chan field for an Intel platform.

If I look at the code I see that the core would limit the number of 
channels to two. But that code needs the CPU_DAI to use 2 channels, 
which I don't see. So is this patch self-contained or do we need an 
additional constraint on the FE?

Thanks
-Pierre