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

[Takashi Iwai]

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 <quic_wcheng at quicinc.com>
> ---
>  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