[PATCH v30 09/30] ALSA: usb-audio: Check for support for requested audio format

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

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

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
 sound/usb/card.c | 32 ++++++++++++++++++++++++++++++++
 sound/usb/card.h |  3 +++
 2 files changed, 35 insertions(+)

diff --git a/sound/usb/card.c b/sound/usb/card.c
index a0087bde684c..6c5b0e02e57b 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -119,6 +119,38 @@ static DEFINE_MUTEX(register_mutex);
 static struct snd_usb_audio *usb_chip[SNDRV_CARDS];
 static struct usb_driver usb_audio_driver;
 
+/*
+ * Checks to see if requested audio profile, i.e sample rate, # of
+ * channels, etc... is supported by the substream associated to the
+ * USB audio device.
+ */
+struct snd_usb_stream *
+snd_usb_find_suppported_substream(int card_idx, struct snd_pcm_hw_params *params,
+				  int direction)
+{
+	struct snd_usb_audio *chip;
+	struct snd_usb_substream *subs;
+	struct snd_usb_stream *as;
+
+	/*
+	 * Register mutex is held when populating and clearing usb_chip
+	 * array.
+	 */
+	guard(mutex)(&register_mutex);
+	chip = usb_chip[card_idx];
+
+	if (chip && enable[card_idx]) {
+		list_for_each_entry(as, &chip->pcm_list, list) {
+			subs = &as->substream[direction];
+			if (snd_usb_find_substream_format(subs, params))
+				return as;
+		}
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(snd_usb_find_suppported_substream);
+
 /*
  * disconnect streams
  * called from usb_audio_disconnect()
diff --git a/sound/usb/card.h b/sound/usb/card.h
index 6ec95b2edf86..4f4f3f39b7fa 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -207,4 +207,7 @@ struct snd_usb_stream {
 	struct list_head list;
 };
 
+struct snd_usb_stream *
+snd_usb_find_suppported_substream(int card_idx, struct snd_pcm_hw_params *params,
+				  int direction);
 #endif /* __USBAUDIO_CARD_H */