Re: [PATCH v13 32/53] ALSA: usb-audio: Check for support for requested audio format
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From: Takashi Iwai <hidden>
Date: 2024-02-06 13:12:51
Also in:
alsa-devel, linux-arm-msm, linux-devicetree, linux-sound, linux-usb, lkml
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 <redacted>
Just cosmetic:
quoted hunk ↗ jump to hunk
+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(®ister_mutex); + chip = usb_chip[card_idx]; + if (!chip) { + mutex_unlock(®ister_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(®ister_mutex); + return as; + } + } + } + mutex_unlock(®ister_mutex);
I prefer having the single lock/unlock call pair, e.g.
struct snd_usb_stream *as, *ret;
ret = NULL;
mutex_lock(®ister_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(®ister_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.
thanks,
Takashi