linux-kernel - Re: [PATCH v37 24/31] ASoC: qcom: qdsp6: Add USB backend ASoC driver for Q6

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Message-ID: <0b8a77f4-2751-3982-3883-dec2ac5804e8@quicinc.com>
Date: Mon, 7 Apr 2025 15:59:56 -0700
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: Stephan Gerhold <stephan.gerhold@...aro.org>
CC: <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
        <perex@...ex.cz>, <conor+dt@...nel.org>, <dmitry.torokhov@...il.com>,
        <corbet@....net>, <broonie@...nel.org>, <lgirdwood@...il.com>,
        <krzk+dt@...nel.org>, <pierre-louis.bossart@...ux.intel.com>,
        <Thinh.Nguyen@...opsys.com>, <tiwai@...e.com>, <robh@...nel.org>,
        <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-sound@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <linux-input@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v37 24/31] ASoC: qcom: qdsp6: Add USB backend ASoC driver
 for Q6

Hi Stephan,

On 4/4/2025 2:54 AM, Stephan Gerhold wrote:
> On Thu, Apr 03, 2025 at 05:27:21PM -0700, Wesley Cheng wrote:
>> Create a USB BE component that will register a new USB port to the ASoC USB
>> framework.  This will handle determination on if the requested audio
>> profile is supported by the USB device currently selected.
>>
>> Check for if the PCM format is supported during the hw_params callback.  If
>> the profile is not supported then the userspace ALSA entity will receive an
>> error, and can take further action.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> ---
>>   include/sound/q6usboffload.h  |  20 +++
>>   sound/soc/qcom/Kconfig        |  12 ++
>>   sound/soc/qcom/qdsp6/Makefile |   1 +
>>   sound/soc/qcom/qdsp6/q6usb.c  | 278 ++++++++++++++++++++++++++++++++++
>>   4 files changed, 311 insertions(+)
>>   create mode 100644 include/sound/q6usboffload.h
>>   create mode 100644 sound/soc/qcom/qdsp6/q6usb.c
>>
>> diff --git a/include/sound/q6usboffload.h b/include/sound/q6usboffload.h
>> new file mode 100644
>> index 000000000000..35ae26ba6509
>> --- /dev/null
>> +++ b/include/sound/q6usboffload.h
>> @@ -0,0 +1,20 @@
>> +/* SPDX-License-Identifier: GPL-2.0
>> + *
>> + * sound/q6usboffload.h -- QDSP6 USB offload
>> + *
>> + * Copyright (c) 2022-2025 Qualcomm Innovation Center, Inc. All rights reserved.
>> + */
>> +
>> +/**
>> + * struct q6usb_offload - USB backend DAI link offload parameters
>> + * @dev: dev handle to usb be
>> + * @domain: allocated iommu domain
>> + * @sid: streamID for iommu
>> + * @intr_num: usb interrupter number
>> + **/
>> +struct q6usb_offload {
>> +	struct device *dev;
>> +	struct iommu_domain *domain;
>> +	long long sid;
> 
> "long long" feels like overkill for sid, given that it's essentially
> either an u8 or -1. I see you just copied this from q6asm-dai.c, but
> unlike q6asm-dai, you don't seem to check for sid < 0 in PATCH 28/31
> (qc_audio_offload.c).
> 
> Looking at the logic in q6asm-dai.c, it feels like this could really
> just be an "u8", since the -1 for "no iommus specified" is effectively
> just handled like sid = 0.
> 

Thanks for the detailed feedback and review.  Will change it accordingly 
as you suggested.

>> +	u16 intr_num;
>> +};
>> [...]
>> diff --git a/sound/soc/qcom/qdsp6/q6usb.c b/sound/soc/qcom/qdsp6/q6usb.c
>> new file mode 100644
>> index 000000000000..cb8c4a62a816
>> --- /dev/null
>> +++ b/sound/soc/qcom/qdsp6/q6usb.c
>> [...]
>> +static int q6usb_dai_dev_probe(struct platform_device *pdev)
>> +{
>> +	struct device_node *node = pdev->dev.of_node;
>> +	struct q6usb_port_data *data;
>> +	struct device *dev = &pdev->dev;
>> +	struct of_phandle_args args;
>> +	int ret;
>> +
>> +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
>> +	if (!data)
>> +		return -ENOMEM;
>> +
>> +	ret = of_property_read_u16(node, "qcom,usb-audio-intr-idx",
>> +				   &data->priv.intr_num);
>> +	if (ret) {
>> +		dev_err(&pdev->dev, "failed to read intr idx.\n");
>> +		return ret;
>> +	}
>> +
>> +	ret = of_parse_phandle_with_fixed_args(node, "iommus", 1, 0, &args);
>> +	if (ret < 0)
>> +		data->priv.sid = -1;
>> +	else
> 
> Could just do if (ret == 0) here and drop the if branch above, if you
> make sid an u8 like I suggested above.
> 

Will do.

>> +		data->priv.sid = args.args[0] & Q6_USB_SID_MASK;
>> +
>> +	data->priv.domain = iommu_get_domain_for_dev(&pdev->dev);
>> +
>> +	data->priv.dev = dev;
>> +	INIT_LIST_HEAD(&data->devices);
> 
> I think you also need devm_mutex_init(&data->lock) or separate
> mutex_init()/mutex_destroy() here, if someone enables
> CONFIG_DEBUG_MUTEXES.
> 

Ah, yes, will explicitly initialize the mutex here.

Thanks
Wesley Cheng