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

[Stephan Gerhold <stephan.gerhold@linaro.org>]

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@quicinc.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.

> +	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.

> +		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.

Thanks,
Stephan