[PATCH v25 32/33] ALSA: usb-audio: Allow for rediscovery of connected USB SND devices

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

In case of notifying SND platform drivers of connection events, some of
these use cases, such as offloading, require an ASoC USB backend device to
be initialized before the events can be handled.  If the USB backend device
has not yet been probed, this leads to missing initial USB audio device
connection events.

Expose an API that traverses the usb_chip array for connected devices, and
to call the respective connection callback registered to the SND platform
driver.

Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
 sound/usb/card.c                  | 21 +++++++++++++++++++++
 sound/usb/card.h                  |  2 ++
 sound/usb/qcom/qc_audio_offload.c |  2 ++
 3 files changed, 25 insertions(+)

diff --git a/sound/usb/card.c b/sound/usb/card.c
index fb548a3abcfc..8c22f6bfdef2 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -155,6 +155,27 @@ int snd_usb_unregister_platform_ops(void)
 }
 EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
 
+/*
+ * in case the platform driver was not ready at the time of USB SND
+ * device connect, expose an API to discover all connected USB devices
+ * so it can populate any dependent resources/structures.
+ */
+void snd_usb_rediscover_devices(void)
+{
+	int i;
+
+	guard(mutex)(&register_mutex);
+
+	if (!platform_ops || !platform_ops->connect_cb)
+		return;
+
+	for (i = 0; i < SNDRV_CARDS; i++) {
+		if (usb_chip[i])
+			platform_ops->connect_cb(usb_chip[i]);
+	}
+}
+EXPORT_SYMBOL_GPL(snd_usb_rediscover_devices);
+
 /*
  * Checks to see if requested audio profile, i.e sample rate, # of
  * channels, etc... is supported by the substream associated to the
diff --git a/sound/usb/card.h b/sound/usb/card.h
index a2ce4463a36f..9fa90f66991f 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -221,4 +221,6 @@ struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
 
 int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops);
 int snd_usb_unregister_platform_ops(void);
+
+void snd_usb_rediscover_devices(void);
 #endif /* __USBAUDIO_CARD_H */
diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
index 8d19aeea09e5..511c799fe402 100644
--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -1925,6 +1925,8 @@ static int __init qc_usb_audio_offload_init(void)
 	if (ret < 0)
 		goto release_qmi;
 
+	snd_usb_rediscover_devices();
+
 	return 0;
 
 release_qmi: