Re: [PATCH v2 07/21] ASoC: ops: Introduce 'soc_set_enum_kctl'

[Ajay Kumar Nandam <ajay.nandam@oss.qualcomm.com>]

On 10/4/2026 11:33 AM, James Calligeros wrote:
> From: Martin Povišer <povik+lin@cutebit.org>
> 
> The new function is to be used to set enumerated controls to desired
> values. It is something a machine driver may call in fixup_controls.
> 
> Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
> Signed-off-by: James Calligeros <jcalligeros99@gmail.com>

> --- a/sound/soc/soc-ops.c
> +++ b/sound/soc/soc-ops.c
> @@ -505,6 +505,75 @@ int snd_soc_deactivate_kctl(struct snd_soc_card *card,
>   }
>   EXPORT_SYMBOL_GPL(snd_soc_deactivate_kctl);
>   
> +static int soc_set_enum_kctl(struct snd_kcontrol *kctl, const char *value)
> +{
> +	struct snd_ctl_elem_value evalue = { 0 };
> +	struct snd_ctl_elem_info info = { 0 };
> +	int sel, i, ret;
> +
> +	ret = kctl->info(kctl, &info);
> +	if (ret < 0)
> +		return ret;
> +

Could this initialize the control IDs before calling the control callbacks?

The normal ALSA write path does not call `put()` with an empty ID: 
`snd_ctl_elem_write()` resolves the control and then calls 
`snd_ctl_build_ioff(&control->id, kctl, index_offset)` before invoking 
the control's `put()` callback. This helper builds a zeroed `struct 
snd_ctl_elem_value` and passes it directly to `kctl->put()`, so 
callbacks that inspect `ucontrol->id.name` see an empty name.

There are existing enum/mux callbacks that branch on 
`ucontrol->id.name`, for example `rt700_mux_put()` and similar SoundWire 
codec mux callbacks. So this helper should probably initialize the 
callback objects from the target control before calling into them, e.g. 
set `info.id = kctl->id` and `evalue.id = kctl->id` before the `info()` 
/ `put()` calls.

While touching this, it may also be worth heap-allocating `struct 
snd_ctl_elem_value`, matching the nearby 
`snd_soc_clip_to_platform_max()` pattern, since the ALSA control value 
struct is fairly large for stack use.


> +	if (info.type != SNDRV_CTL_ELEM_TYPE_ENUMERATED)
> +		return -EINVAL;
> +
> +	for (sel = 0; sel < info.value.enumerated.items; sel++) {
> +		info.value.enumerated.item = sel;
> +		ret = kctl->info(kctl, &info);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (!strcmp(value, info.value.enumerated.name))
> +			break;
> +	}
> +
> +	if (sel == info.value.enumerated.items)
> +		return -EINVAL;
> +
> +	for (i = 0; i < info.count; i++)
> +		evalue.value.enumerated.item[i] = sel;
> +
> +	if (kctl->put)
> +		return kctl->put(kctl, &evalue);
> +	else
> +		return -EINVAL;
> +}
> +
> +/**
> + * snd_soc_set_enum_kctl - Set enumerated control matching a name
> + *
> + * @card: where to look for the controls
> + * @name: name
> + * @value: string value to set the controls to
> + *
> + * Return 0 on success, else error.
> + */
> +int snd_soc_set_enum_kctl(struct snd_soc_card *card,
> +	const char *name, const char *value)
> +{
> +	struct snd_kcontrol *kctl;
> +	int ret = -EINVAL;
> +
> +	/* Sanity check for name */
> +	if (unlikely(!name))
> +		return -EINVAL;
> +
> +	kctl = snd_soc_card_get_kcontrol(card, name);
> +
> +	if (kctl) {
> +		ret = soc_set_enum_kctl(kctl, value);
> +		if (ret)
> +			return ret;
> +	} else {
> +		dev_dbg(card->dev, "Tried to set unknown control '%s' to '%s'\n",
> +			name, value);
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_set_enum_kctl);
> +
>   int snd_soc_bytes_info(struct snd_kcontrol *kcontrol,
>   		       struct snd_ctl_elem_info *uinfo)
>   {
>