[v4,19/32] sound: usb: card: Check for support for requested audio format

Commit Message

Wesley Cheng July 25, 2023, 2:34 a.m. UTC

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 <[e-mail]>
---
 sound/usb/card.c | 28 ++++++++++++++++++++++++++++
 sound/usb/card.h |  8 ++++++++
 2 files changed, 36 insertions(+)

Comments

Takashi Iwai July 25, 2023, 6:57 a.m. UTC | #1

On Tue, 25 Jul 2023 04:34:03 +0200,
Wesley Cheng wrote:
> 
> 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 <[e-mail]>
> ---
>  sound/usb/card.c | 28 ++++++++++++++++++++++++++++
>  sound/usb/card.h |  8 ++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index a3fad66a3337..365f6d978608 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -142,6 +142,34 @@ int snd_usb_unregister_platform_ops(void)
>  }
>  EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
>  
> +struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
> +			struct snd_pcm_hw_params *params, int direction)
> +{

Please add a comment what this function does.


> +	struct snd_usb_audio *chip = usb_chip[card_idx];

Is the dereference safe without locking?
If the call is supposed to be allowed only in a safe situation, it
should be mentioned in the function description.


thanks,

Takashi

Patch

diff --git a/sound/usb/card.c b/sound/usb/card.c
index a3fad66a3337..365f6d978608 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -142,6 +142,34 @@  int snd_usb_unregister_platform_ops(void)
 }
 EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
 
+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 = usb_chip[card_idx];
+	struct snd_usb_substream *subs = NULL;
+	struct snd_usb_stream *as;
+	const struct audioformat *fmt;
+
+	if (!chip)
+		return NULL;
+
+	mutex_lock(&chip->mutex);
+	if (enable[card_idx]) {
+		list_for_each_entry(as, &chip->pcm_list, list) {
+			subs = &as->substream[direction];
+			fmt = find_substream_format(subs, params);
+			if (fmt) {
+				mutex_unlock(&chip->mutex);
+				return as;
+			}
+		}
+	}
+	mutex_unlock(&chip->mutex);
+
+	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 c48744724f7d..6d0f76ffec9d 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -216,6 +216,8 @@  struct snd_usb_platform_ops {
 #if IS_ENABLED(CONFIG_SND_USB_AUDIO)
 int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops);
 int snd_usb_unregister_platform_ops(void);
+struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
+			struct snd_pcm_hw_params *params, int direction);
 #else
 static int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
 {
@@ -226,5 +228,11 @@  static int snd_usb_unregister_platform_ops(void)
 {
 	return -EOPNOTSUPP;
 }
+
+static struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
+			struct snd_pcm_hw_params *params, int direction)
+{
+	return NULL;
+}
 #endif /* IS_ENABLED(CONFIG_SND_USB_AUDIO) */
 #endif /* __USBAUDIO_CARD_H */