Re: [PATCH v6] ALSA: control: Verify put() result when in debug mode

[Takashi Iwai <tiwai@suse.de>]

On Mon, 23 Feb 2026 15:49:37 +0100,
Cezary Rojewski wrote:
> 
> The put() operation is expected to return:
> 1) 0 on success if no changes were made
> 2) 1 on success if changes were made
> 3) error code otherwise
> 
> Currently 2) is usually ignored when writing control-operations. While
> forcing compliance is not an option right now, make it easier for
> developers to adhere to the expectations and notice problems by logging
> them when CONFIG_SND_CTL_DEBUG is enabled.
> 
> Due to large size of struct snd_ctl_elem_value, 'value_buf' is provided
> as a reusable buffer for kctl->put() verification. This prevents
> exhausting the stack when verifying the operation.
> 
> From user perspective, patch introduces a new trace/events category
> 'snd_ctl' containing a single 'snd_ctl_put' event type. Log sample:
> 
>   amixer-1107    [002] .....   9.553687: snd_ctl_put: success: expected=0, actual=0 for ctl numid=1, iface=MIXER, name='Master Playback Volume', card id=0
>   amixer-1108    [003] .....   9.498897: snd_ctl_put: success: expected=1, actual=1 for ctl numid=1, iface=MIXER, name='Master Playback Volume', card id=0
>   amixer-1111    [001] .....   9.882768: snd_ctl_put: success: expected=1, actual=1 for ctl numid=5, iface=MIXER, name='Loopback Mute', card id=0
>   amixer-1114    [002] .....   9.212184: snd_ctl_put: fail: expected=1, actual=0 for ctl numid=5, iface=MIXER, name='Loopback Mute', card id=0
> 
> Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>

Looks almost good, just a minor nitpicking:

> --- a/sound/core/init.c
> +++ b/sound/core/init.c
(snip)
> @@ -537,6 +542,9 @@ void snd_card_disconnect(struct snd_card *card)
>  		synchronize_irq(card->sync_irq);
>  
>  	snd_info_card_disconnect(card);
> +#ifdef CONFIG_SND_CTL_DEBUG
> +	kfree(card->value_buf);
> +#endif
>  #ifdef CONFIG_SND_DEBUG
>  	debugfs_remove(card->debugfs_root);
>  	card->debugfs_root = NULL;

IMO, it's better to be put in snd_card_do_free() which is the place to
release the actual resources.


thanks,

Takashi