Re: [PATCH] ALSA: usb-audio: use kzalloc_flex

[Takashi Iwai]

On Thu, 12 Mar 2026 00:27:48 +0100,
Rosen Penev wrote:
> 
> Saves one allocation by using a flexible array member.

As it's a fixed size array, it doesn't have to be a flex array at all,
so it can be even simpler.


thanks,

Takashi

> 
> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> ---
>  sound/usb/mixer.c | 22 +++++++---------------
>  sound/usb/mixer.h |  5 +++--
>  2 files changed, 10 insertions(+), 17 deletions(-)
> 
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index 7007e0c9489b..337815b9e72c 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -1393,7 +1393,7 @@ static int mixer_ctl_feature_info(struct snd_kcontrol *kcontrol,
>  		if (!cval->initialized) {
>  			get_min_max_with_quirks(cval, 0, kcontrol);
>  			if (cval->initialized && cval->dBmin >= cval->dBmax) {
> -				kcontrol->vd[0].access &= 
> +				kcontrol->vd[0].access &=
>  					~(SNDRV_CTL_ELEM_ACCESS_TLV_READ |
>  					  SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK);
>  				snd_ctl_notify(cval->head.mixer->chip->card,
> @@ -3006,15 +3006,12 @@ static void snd_usb_mixer_free(struct usb_mixer_interface *mixer)
>  	snd_usb_mixer_disconnect(mixer);
>  
>  	/* Unregister controls first, snd_ctl_remove() frees the element */
> -	if (mixer->id_elems) {
> -		for (id = 0; id < MAX_ID_ELEMS; id++) {
> -			for (list = mixer->id_elems[id]; list; list = next) {
> -				next = list->next_id_elem;
> -				if (list->kctl)
> -					snd_ctl_remove(mixer->chip->card, list->kctl);
> -			}
> +	for (id = 0; id < MAX_ID_ELEMS; id++) {
> +		for (list = mixer->id_elems[id]; list; list = next) {
> +			next = list->next_id_elem;
> +			if (list->kctl)
> +				snd_ctl_remove(mixer->chip->card, list->kctl);
>  		}
> -		kfree(mixer->id_elems);
>  	}
>  	if (mixer->urb) {
>  		kfree(mixer->urb->transfer_buffer);
> @@ -3652,16 +3649,11 @@ int snd_usb_create_mixer(struct snd_usb_audio *chip, int ctrlif)
>  
>  	strscpy(chip->card->mixername, "USB Mixer");
>  
> -	mixer = kzalloc_obj(*mixer);
> +	mixer = kzalloc_flex(*mixer, id_elems, MAX_ID_ELEMS);
>  	if (!mixer)
>  		return -ENOMEM;
>  	mixer->chip = chip;
>  	mixer->ignore_ctl_error = !!(chip->quirk_flags & QUIRK_FLAG_IGNORE_CTL_ERROR);
> -	mixer->id_elems = kzalloc_objs(*mixer->id_elems, MAX_ID_ELEMS);
> -	if (!mixer->id_elems) {
> -		kfree(mixer);
> -		return -ENOMEM;
> -	}
>  
>  	mixer->hostif = &usb_ifnum_to_if(chip->dev, ctrlif)->altsetting[0];
>  	switch (get_iface_desc(mixer->hostif)->bInterfaceProtocol) {
> diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
> index 167fbfcf01ac..30dd30b925fc 100644
> --- a/sound/usb/mixer.h
> +++ b/sound/usb/mixer.h
> @@ -19,8 +19,6 @@ struct usb_mixer_interface {
>  	struct list_head list;
>  	unsigned int ignore_ctl_error;
>  	struct urb *urb;
> -	/* array[MAX_ID_ELEMS], indexed by unit id */
> -	struct usb_mixer_elem_list **id_elems;
>  
>  	/* the usb audio specification version this interface complies to */
>  	int protocol;
> @@ -42,6 +40,9 @@ struct usb_mixer_interface {
>  	void *private_data;
>  	void (*private_free)(struct usb_mixer_interface *mixer);
>  	void (*private_suspend)(struct usb_mixer_interface *mixer);
> +
> +	/* array[MAX_ID_ELEMS], indexed by unit id */
> +	struct usb_mixer_elem_list *id_elems[];
>  };
>  
>  #define MAX_CHANNELS	16	/* max logical channels */
> -- 
> 2.53.0
>