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

[Cezary Rojewski <cezary.rojewski@intel.com>]

On 2026-02-24 2:21 PM, Jaroslav Kysela wrote:
> On 2/23/26 15:49, 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
> 
> Index (and maybe device/subdevice) numbers are missing to get full 
> control identification to follow amixer. Also, "card id" is usually 
> referred to automatically or manually assigned ASCII card identifier/ 
> alias (like USB-audio or PCH). I would just use 'card=<number>' in 
> TP_printk.


If the message length isn't a problem, then I'm going to add all of them 
in v7.