[PATCH v4 06/32] ASoC: Add SOC USB APIs for adding an USB backend

[Wesley Cheng]

Some platforms may have support for offloading USB audio devices to a
dedicated audio DSP.  Introduce a set of APIs that allow for management of
USB sound card and PCM devices enumerated by the USB SND class driver.
This allows for the ASoC components to be aware of what USB devices are
available for offloading.

Signed-off-by: Wesley Cheng <quic_wcheng at quicinc.com>
---
 include/sound/soc-usb.h |  35 ++++++++
 sound/soc/Makefile      |   2 +-
 sound/soc/soc-usb.c     | 180 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 216 insertions(+), 1 deletion(-)
 create mode 100644 include/sound/soc-usb.h
 create mode 100644 sound/soc/soc-usb.c

diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
new file mode 100644
index 000000000000..378992ea07bd
--- /dev/null
+++ b/include/sound/soc-usb.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifndef __LINUX_SND_SOC_USB_H
+#define __LINUX_SND_SOC_USB_H
+
+/**
+ * struct snd_soc_usb
+ * @list - list head for SND SOC struct list
+ * @dev - USB backend device reference
+ * @component - reference to DAPM component
+ * @connection_status_cb - callback to notify connection events
+ * @priv_data - driver data
+ **/
+struct snd_soc_usb {
+	struct list_head list;
+	struct device *dev;
+	struct snd_soc_component *component;
+	int (*connection_status_cb)(struct snd_soc_usb *usb, int card_idx,
+				int connected);
+	void *priv_data;
+};
+
+int snd_soc_usb_connect(struct device *usbdev, int card_idx);
+int snd_soc_usb_disconnect(struct device *usbdev);
+void snd_soc_usb_set_priv_data(struct device *dev, void *priv);
+void *snd_soc_usb_get_priv_data(struct device *usbdev);
+
+struct snd_soc_usb *snd_soc_usb_add_port(struct device *dev, void *priv,
+			int (*connection_cb)(struct snd_soc_usb *usb, int card_idx,
+			int connected));
+int snd_soc_usb_remove_port(struct device *dev);
+#endif
diff --git a/sound/soc/Makefile b/sound/soc/Makefile
index 507eaed1d6a1..3305ceb59d84 100644
--- a/sound/soc/Makefile
+++ b/sound/soc/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-snd-soc-core-objs := soc-core.o soc-dapm.o soc-jack.o soc-utils.o soc-dai.o soc-component.o
+snd-soc-core-objs := soc-core.o soc-dapm.o soc-jack.o soc-usb.o soc-utils.o soc-dai.o soc-component.o
 snd-soc-core-objs += soc-pcm.o soc-devres.o soc-ops.o soc-link.o soc-card.o
 snd-soc-core-$(CONFIG_SND_SOC_COMPRESS) += soc-compress.o
 
diff --git a/sound/soc/soc-usb.c b/sound/soc/soc-usb.c
new file mode 100644
index 000000000000..4293451cdd49
--- /dev/null
+++ b/sound/soc/soc-usb.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2022-2023 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);
+
+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);
+	list_for_each_entry(ctx, &usb_ctx_list, list) {
+		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
+ * @dev: device reference
+ *
+ * Fetch the private data stored in the USB SND SOC structure.
+ *
+ */
+void *snd_soc_usb_get_priv_data(struct device *dev)
+{
+	struct snd_soc_usb *ctx;
+
+	ctx = snd_soc_find_usb_ctx(dev);
+	if (!ctx) {
+		/* Check if backend device */
+		list_for_each_entry(ctx, &usb_ctx_list, list) {
+			if (dev->of_node == ctx->dev->of_node)
+				goto out;
+		}
+		ctx = NULL;
+	}
+out:
+	return ctx ? ctx->priv_data : NULL;
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_get_priv_data);
+
+/**
+ * snd_soc_usb_add_port() - Add a USB backend port
+ * @dev: USB backend device
+ * @priv: private data
+ * @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, void *priv,
+			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;
+	usb->priv_data = priv;
+
+	mutex_lock(&ctx_mutex);
+	list_add_tail(&usb->list, &usb_ctx_list);
+	mutex_unlock(&ctx_mutex);
+
+	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_disconnect() - Notification of USB device disconnection
+ * @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);