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

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