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

[Wesley Cheng]

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@xxxxxxxxxxx>
> > ---
> >   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