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Message-ID: <9d0ba8c8-9c8f-a45a-cf14-5d1829273cfa@quicinc.com>
Date: Wed, 8 May 2024 17:13:37 -0700
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Subject: Re: [PATCH v21 33/39] ASoC: usb: Fetch ASoC sound card information
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To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        <srinivas.kandagatla@linaro.org>, <mathias.nyman@intel.com>,
        <perex@perex.cz>, <conor+dt@kernel.org>, <corbet@lwn.net>,
        <lgirdwood@gmail.com>, <andersson@kernel.org>, <krzk+dt@kernel.org>,
        <gregkh@linuxfoundation.org>, <Thinh.Nguyen@synopsys.com>,
        <broonie@kernel.org>, <bgoswami@quicinc.com>, <tiwai@suse.com>,
        <bagasdotme@gmail.com>, <robh@kernel.org>, <konrad.dybcio@linaro.org>
CC: <linux-kernel@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-sound@vger.kernel.org>, <linux-usb@vger.kernel.org>,
        <linux-arm-msm@vger.kernel.org>, <linux-doc@vger.kernel.org>,
        <alsa-devel@alsa-project.org>
References: <20240507195116.9464-1-quic_wcheng@quicinc.com>
 <20240507195116.9464-34-quic_wcheng@quicinc.com>
 <6fe8f489-d8a2-4951-96fa-875ac9b29d23@linux.intel.com>
From: Wesley Cheng <quic_wcheng@quicinc.com>
In-Reply-To: <6fe8f489-d8a2-4951-96fa-875ac9b29d23@linux.intel.com>
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Hi Pierre,

On 5/7/2024 2:33 PM, Pierre-Louis Bossart wrote:
> 
>> +/**
>> + * snd_soc_usb_device_offload_available() - Fetch BE DAI link sound card
>> + * @dev: the device to find in SOC USB
>> + *
>> + * Finds the component linked to a specific SOC USB instance, and returns
>> + * the sound card number for the platform card supporting offloading.
>> + *
>> + */
>> +int snd_soc_usb_device_offload_available(struct device *dev)
>> +{
>> +	struct snd_soc_usb *ctx;
>> +
>> +	ctx = snd_soc_find_usb_ctx(dev);
>> +	if (!ctx)
>> +		return -ENODEV;
>> +
>> +	return ctx->component->card->snd_card->number;
>> +}
> 
> Presumably there's a notification to help applications discard this
> information on removal?

If the platform/ASoC sound card is removed then the USB BE DAI is going 
to be unregistered from SOC USB.  This would lead to the 
snd_soc_find_usb_ctx() to return with -ENODEV to the USB SND offload 
kcontrol call.

Thanks
Wesley Cheng