[RFC PATCH 10/14] sound: usb: card: Check for support for requested audio format

[Wesley Cheng <quic_wcheng@quicinc.com>]

Allow for checks on a specific USB audio device to see if a requested PCM
format is supported.  This is needed for support for when playback is
initiated by the ASoC USB backend path.

Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
---
 sound/usb/card.c | 19 +++++++++++++++++++
 sound/usb/card.h |  3 +++
 2 files changed, 22 insertions(+)

diff --git a/sound/usb/card.c b/sound/usb/card.c
index 396e5a34e23b..9b8d2ed308c8 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -133,6 +133,25 @@ int snd_usb_unregister_vendor_ops(void)
 }
 EXPORT_SYMBOL_GPL(snd_usb_unregister_vendor_ops);
 
+struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
+			struct snd_pcm_hw_params *params, int direction)
+{
+	struct snd_usb_stream *as;
+	struct snd_usb_substream *subs = NULL;
+	const struct audioformat *fmt;
+
+	if (usb_chip[card_idx] && enable[card_idx]) {
+		list_for_each_entry(as, &usb_chip[card_idx]->pcm_list, list) {
+			subs = &as->substream[direction];
+			fmt = find_substream_format(subs, params);
+			if (fmt)
+				return as;
+		}
+	}
+
+	return 0;
+}
+
 /*
  * disconnect streams
  * called from usb_audio_disconnect()
diff --git a/sound/usb/card.h b/sound/usb/card.h
index a785bb256b0d..d4936b6054fc 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -213,4 +213,7 @@ struct snd_usb_vendor_ops {
 
 int snd_usb_register_vendor_ops(struct snd_usb_vendor_ops *ops);
 int snd_usb_unregister_vendor_ops(void);
+
+struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
+			struct snd_pcm_hw_params *params, int direction);
 #endif /* __USBAUDIO_CARD_H */