Re: [RFC PATCH v2 07/22] ASoC: Add SOC USB APIs for adding an USB backend

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jan 25, 2023 at 07:14:09PM -0800, Wesley Cheng wrote:
> diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
> new file mode 100644
> index 000000000000..ec422a8a834f
> --- /dev/null
> +++ b/include/sound/soc-usb.h
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * Copyright (c) 2022 Qualcomm Innovation Center, Inc. All rights reserved.

It is now 2023 :)

> + */
> +
> +#ifndef __LINUX_SND_SOC_USB_H
> +#define __LINUX_SND_SOC_USB_H
> +
> +/**
> + * struct snd_soc_usb
> + * @component - Reference to DAPM component
> + * @connection_status_cb - callback to notify connection events
> + * @priv_data - vendor data

You do not document all items in the structure so you will get build
warnings :(

And what exactly is "vendor data"?  You use that term in a few places in
this series, there is no such thing as a "vendor" in the kernel.  This
could be a device or driver specific data, but not a "vendor".

> --- /dev/null
> +++ b/sound/soc/soc-usb.c
> @@ -0,0 +1,202 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2022 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +#include <linux/of.h>
> +#include <linux/usb.h>
> +#include <sound/soc.h>
> +#include <sound/soc-usb.h>
> +#include "../usb/card.h"
> +
> +static DEFINE_MUTEX(ctx_mutex);
> +static LIST_HEAD(usb_ctx_list);

What is this a list of?  Why a list?  This should be dynamic and tied to
the device itself somehow, not a separate list you have to walk.

> +
> +#define for_each_usb_ctx(ctx)			\
> +	list_for_each_entry(ctx, &usb_ctx_list, list)

No need for a #define like this, just spell it out.


> +
> +static struct device_node *snd_soc_find_phandle(struct device *dev)
> +{
> +	struct device_node *node;
> +
> +	node = of_parse_phandle(dev->of_node, "usb-soc-be", 0);
> +	if (!node)
> +		return ERR_PTR(-ENODEV);
> +
> +	return node;
> +}
> +
> +static struct snd_soc_usb *snd_soc_find_usb_ctx(struct device *dev)
> +{
> +	struct device_node *node;
> +	struct snd_soc_usb *ctx = NULL;
> +
> +	node = snd_soc_find_phandle(dev);
> +	if (IS_ERR(node))
> +		return NULL;
> +
> +	mutex_lock(&ctx_mutex);
> +	for_each_usb_ctx(ctx) {
> +		if (ctx->dev->of_node == node) {
> +			of_node_put(node);
> +			mutex_unlock(&ctx_mutex);
> +			return ctx;
> +		}
> +	}
> +	of_node_put(node);
> +	mutex_unlock(&ctx_mutex);
> +
> +	return NULL;
> +}
> +
> +/**
> + * snd_soc_usb_get_priv_data() - Retrieve private data stored
> + * @usbdev: USB bus sysdev
> + *
> + * Fetch the private data stored in the USB SND SOC structure.  This is
> + * intended to be called by the USB offloading class driver, in order to
> + * attain parameters about the USB backend device.
> + *
> + */
> +void *snd_soc_usb_get_priv_data(struct device *usbdev)
> +{
> +	struct snd_soc_usb *ctx;
> +
> +	if (!usbdev)
> +		return NULL;

How could usbdev ever be NULL?

> +
> +	ctx = snd_soc_find_usb_ctx(usbdev);
> +
> +	return ctx ? ctx->priv_data : NULL;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_get_priv_data);
> +
> +/**
> + * snd_soc_usb_set_priv_data() - Set private data stored
> + * @dev: USB backend device
> + * @priv: private data to store
> + *
> + * Save data describing the USB backend device parameters.  This is intended
> + * to be called by the ASoC USB backend driver.
> + *
> + */
> +void snd_soc_usb_set_priv_data(struct device *dev, void *priv)
> +{
> +	struct snd_soc_usb *ctx;


Why does this function take a "struct device" but the get function take
a USB device?

> +
> +	mutex_lock(&ctx_mutex);
> +	for_each_usb_ctx(ctx) {
> +		if (dev->of_node == ctx->dev->of_node) {
> +			ctx->priv_data = priv;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&ctx_mutex);
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_set_priv_data);
> +
> +/**
> + * snd_soc_usb_add_port() - Add a USB backend port
> + * @dev: USB backend device
> + * @connection_cb: connection status callback
> + *
> + * Register a USB backend device to the SND USB SOC framework.  Memory is
> + * allocated as part of the USB backend device.
> + *
> + */
> +struct snd_soc_usb *snd_soc_usb_add_port(struct device *dev,
> +			int (*connection_cb)(struct snd_soc_usb *usb, int card_idx,
> +			int connected))
> +{
> +	struct snd_soc_usb *usb;
> +
> +	usb = devm_kzalloc(dev, sizeof(*usb), GFP_KERNEL);
> +	if (!usb)
> +		return ERR_PTR(-ENOMEM);
> +
> +	usb->connection_status_cb = connection_cb;
> +	usb->dev = dev;
> +
> +	mutex_lock(&ctx_mutex);
> +	list_add_tail(&usb->list, &usb_ctx_list);
> +	mutex_unlock(&ctx_mutex);

Again, why a list?


> +
> +	return usb;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_add_port);
> +
> +/**
> + * snd_soc_usb_remove_port() - Remove a USB backend port
> + * @dev: USB backend device
> + *
> + * Remove a USB backend device from USB SND SOC.  Memory is freed when USB
> + * backend is removed.
> + *
> + */
> +int snd_soc_usb_remove_port(struct device *dev)
> +{
> +	struct snd_soc_usb *ctx, *tmp;
> +
> +	mutex_lock(&ctx_mutex);
> +	list_for_each_entry_safe(ctx, tmp, &usb_ctx_list, list) {
> +		if (ctx->dev == dev) {
> +			list_del(&ctx->list);
> +			break;
> +		}
> +	}
> +	mutex_unlock(&ctx_mutex);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_remove_port);
> +
> +/**
> + * snd_soc_usb_connect() - Notification of USB device connection
> + * @usbdev: USB bus device
> + * @card_idx: USB SND card instance
> + *
> + * Notify of a new USB SND device connection.  The card_idx can be used to
> + * handle how the USB backend selects, which device to enable offloading on.
> + *
> + */
> +int snd_soc_usb_connect(struct device *usbdev, int card_idx)
> +{
> +	struct snd_soc_usb *ctx;
> +
> +	if (!usbdev)
> +		return -ENODEV;
> +
> +	ctx = snd_soc_find_usb_ctx(usbdev);
> +	if (!ctx)
> +		return -ENODEV;
> +
> +	if (ctx->connection_status_cb)
> +		ctx->connection_status_cb(ctx, card_idx, 1);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_connect);
> +
> +/**
> + * snd_soc_usb_connect() - Notification of USB device connection
> + * @usbdev: USB bus device
> + *
> + * Notify of a new USB SND device disconnection to the USB backend.
> + *
> + */
> +int snd_soc_usb_disconnect(struct device *usbdev)
> +{
> +	struct snd_soc_usb *ctx;
> +
> +	if (!usbdev)
> +		return -ENODEV;
> +
> +	ctx = snd_soc_find_usb_ctx(usbdev);
> +	if (!ctx)
> +		return -ENODEV;
> +
> +	if (ctx->connection_status_cb)
> +		ctx->connection_status_cb(ctx, -1, 0);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_disconnect);

Meta-comment, why are all of these in the sound directory?  They are
only operating on USB devices, nothing else.  So why here?

thanks,

greg k-h