[PATCH v22 33/38] ASoC: usb: Fetch ASoC sound card information

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

For USB sound to expose mixer controls to fetch information about the ASoC
sound card, add an API that returns the platform sound card number that is
registered with SOC USB.  Knowing this allows for applications to further
query about the offload status.

Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
 include/sound/soc-usb.h |  6 ++++++
 sound/soc/soc-usb.c     | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
index 8e94c1991819..ab5ade4942d5 100644
--- a/include/sound/soc-usb.h
+++ b/include/sound/soc-usb.h
@@ -85,6 +85,7 @@ int snd_soc_usb_find_supported_format(int card_idx,
 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 *dev);
+int snd_soc_usb_device_offload_available(struct device *dev);
 
 int snd_soc_usb_prepare_session(struct snd_soc_usb *usb, int card_idx, int pcm_idx);
 int snd_soc_usb_shutdown_session(struct snd_soc_usb *usb, int session_id);
@@ -129,6 +130,11 @@ static inline void *snd_soc_usb_find_priv_data(struct device *dev)
 	return NULL;
 }
 
+static inline int snd_soc_usb_device_offload_available(struct device *dev)
+{
+	return -ENODEV;
+}
+
 static inline int snd_soc_usb_prepare_session(struct snd_soc_usb *usb, int card_idx,
 						int pcm_idx)
 {
diff --git a/sound/soc/soc-usb.c b/sound/soc/soc-usb.c
index 0baba34910b5..d50bcb9f379e 100644
--- a/sound/soc/soc-usb.c
+++ b/sound/soc/soc-usb.c
@@ -503,6 +503,26 @@ int snd_soc_usb_find_supported_format(int card_idx,
 }
 EXPORT_SYMBOL_GPL(snd_soc_usb_find_supported_format);
 
+/**
+ * snd_soc_usb_device_offload_available() - Fetch BE DAI link sound card
+ * @dev: the device to find in SOC USB
+ *
+ * Finds the component linked to a specific SOC USB instance, and returns
+ * the sound card number for the platform card supporting offloading.
+ *
+ */
+int snd_soc_usb_device_offload_available(struct device *dev)
+{
+	struct snd_soc_usb *ctx;
+
+	ctx = snd_soc_find_usb_ctx(dev);
+	if (!ctx)
+		return -ENODEV;
+
+	return ctx->component->card->snd_card->number;
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_device_offload_available);
+
 /**
  * snd_soc_usb_allocate_port() - allocate a SOC USB device
  * @component: USB DPCM backend DAI component