ASoC: Add SoC USB APIs for adding an USB backend

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.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250409194804.3773260-15-quic_wcheng@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 93 insertions, 0 deletions

diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
new file mode 100644
index 000000000000..a7be5d05218f
--- /dev/null
+++ b/include/sound/soc-usb.h
@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (c) 2022-2025 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifndef __LINUX_SND_SOC_USB_H
+#define __LINUX_SND_SOC_USB_H
+
+#include <sound/soc.h>
+
+/**
+ * struct snd_soc_usb_device - SoC USB representation of a USB sound device
+ * @card_idx: sound card index associated with USB device
+ * @chip_idx: USB sound chip array index
+ * @cpcm_idx: capture PCM index array associated with USB device
+ * @ppcm_idx: playback PCM index array associated with USB device
+ * @num_capture: number of capture streams
+ * @num_playback: number of playback streams
+ * @list: list head for SoC USB devices
+ **/
+struct snd_soc_usb_device {
+	int card_idx;
+	int chip_idx;
+
+	/* PCM index arrays */
+	unsigned int *cpcm_idx; /* TODO: capture path is not tested yet */
+	unsigned int *ppcm_idx;
+	int num_capture; /* TODO: capture path is not tested yet */
+	int num_playback;
+
+	struct list_head list;
+};
+
+/**
+ * struct snd_soc_usb - representation of a SoC USB backend entity
+ * @list: list head for SND SOC struct list
+ * @component: reference to ASoC component
+ * @connection_status_cb: callback to notify connection events
+ * @priv_data: driver data
+ **/
+struct snd_soc_usb {
+	struct list_head list;
+	struct snd_soc_component *component;
+	int (*connection_status_cb)(struct snd_soc_usb *usb,
+				    struct snd_soc_usb_device *sdev,
+				    bool connected);
+	void *priv_data;
+};
+
+#if IS_ENABLED(CONFIG_SND_SOC_USB)
+int snd_soc_usb_connect(struct device *usbdev, struct snd_soc_usb_device *sdev);
+int snd_soc_usb_disconnect(struct device *usbdev, struct snd_soc_usb_device *sdev);
+void *snd_soc_usb_find_priv_data(struct device *usbdev);
+
+struct snd_soc_usb *snd_soc_usb_allocate_port(struct snd_soc_component *component,
+					      void *data);
+void snd_soc_usb_free_port(struct snd_soc_usb *usb);
+void snd_soc_usb_add_port(struct snd_soc_usb *usb);
+void snd_soc_usb_remove_port(struct snd_soc_usb *usb);
+#else
+static inline int snd_soc_usb_connect(struct device *usbdev,
+				      struct snd_soc_usb_device *sdev)
+{
+	return -ENODEV;
+}
+
+static inline int snd_soc_usb_disconnect(struct device *usbdev,
+					 struct snd_soc_usb_device *sdev)
+{
+	return -EINVAL;
+}
+
+static inline void *snd_soc_usb_find_priv_data(struct device *usbdev)
+{
+	return NULL;
+}
+
+static inline struct snd_soc_usb *
+snd_soc_usb_allocate_port(struct snd_soc_component *component, void *data)
+{
+	return ERR_PTR(-ENOMEM);
+}
+
+static inline void snd_soc_usb_free_port(struct snd_soc_usb *usb)
+{ }
+
+static inline void snd_soc_usb_add_port(struct snd_soc_usb *usb)
+{ }
+
+static inline void snd_soc_usb_remove_port(struct snd_soc_usb *usb)
+{ }
+#endif /* IS_ENABLED(CONFIG_SND_SOC_USB) */
+#endif /*__LINUX_SND_SOC_USB_H */