Re: [PATCH v13 32/53] ALSA: usb-audio: Check for support for requested audio format

Wesley Cheng
2024-02-07T00:08:54Z

Hi Takashi,

On 2/6/2024 5:12 AM, Takashi Iwai wrote:
> On Sat, 03 Feb 2024 03:36:24 +0100,
> 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 when playback is
>> initiated by the ASoC USB backend path.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
>
> Just cosmetic:
>
>> +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;
>> + const struct audioformat *fmt;
>> +
>> + /*
>> + * Register mutex is held when populating and clearing usb_chip
>> + * array.
>> + */
>> + mutex_lock(&register_mutex);
>> + chip = usb_chip[card_idx];
>> + if (!chip) {
>> + mutex_unlock(&register_mutex);
>> + return NULL;
>> + }
>> +
>> + if (enable[card_idx]) {
>> + list_for_each_entry(as, &chip->pcm_list, list) {
>> + subs = &as->substream[direction];
>> + fmt = snd_usb_find_substream_format(subs, params);
>> + if (fmt) {
>> + mutex_unlock(&register_mutex);
>> + return as;
>> + }
>> + }
>> + }
>> + mutex_unlock(&register_mutex);
>
> I prefer having the single lock/unlock call pair, e.g.
>
> struct snd_usb_stream *as, *ret;
>
> ret = NULL;
> mutex_lock(&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)) {
> ret = as;
> break;
> }
> }
> }
> mutex_unlock(&register_mutex);
> return ret;
> }
>
> In this case, we shouldn't reuse "as" for the return value since it
> can be non-NULL after the loop end.
>
>
Sure will do, thanks for taking a look.

Thanks
Wesley Cheng