[alsa-devel] focusrite scarlett 18i20 : Mixer controls with corrupted names for

[Stefan Sauer]

Am 25.06.19 um 09:54 schrieb Takashi Iwai:
> On Sat, 22 Jun 2019 22:55:25 +0200,
> Stefan Sauer wrote:
>>
>> So the first 8 controls are added somewhere else. Looks like this is from
>> mixer.c and after
>> echo -n 'file sound/usb/mixer.c +p' >/sys/kernel/debug/dynamic_debug/control
>> I get
>> [ 4405.855432] usb 1-2: [51] PU [KKKKKKKKKKKKKÃÃÃÃÃÃÃÃÃÃÃ Switch] ch = 1, val = 0/1
>> [ 4405.856423] usb 1-2: [52] PU [ Switch] ch = 1, val = 0/1
> 
> This indicates that these weird names come from the two extension
> units id 51 and 52.
> Could you put some debug print in build_audio_procunit() like below?

I traced it down to this part from sound/usb/mixer.c:
nameid = uac_processing_unit_iProcessing(desc, state->mixer->protocol);
usb_audio_dbg(state->chip, "desc->bUnitID=%d, proto=%d, nameid=%d\n",
 	      desc->bUnitID, state->mixer->protocol, nameid);
len = 0;
if (nameid) {
	len = snd_usb_copy_string_desc(state->chip,
				       nameid,
				       kctl->id.name,
				       sizeof(kctl->id.name));
	usb_audio_dbg(state->chip, "nameid=%d, len=%d, fallback name='%s'\n",
 		      nameid, len, name);
}

[ 6241.045734] usb 1-2: desc->bUnitID=51, proto=32, nameid=90
[ 6241.045861] usb 1-2: nameid=90, len=35, fallback name='Extension Unit'
[ 6241.045868] usb 1-2: [51] PU [KKKKKKKKKKKKKÃÃÃÃÃÃÃÃÃÃÃ Switch] ch = 1, val = 0/1
[ 6241.046745] usb 1-2: desc->bUnitID=52, proto=32, nameid=82
[ 6241.046857] usb 1-2: nameid=82, len=1, fallback name='Extension Unit'
[ 6241.046862] usb 1-2: [52] PU [ Switch] ch = 1, val = 0/1

The device is using UAC_VERSION_2. The code in include/uapi/linux/usb/audio.h is
a bit hard to read since uac_mixer_unit_descriptor has a variable length and the
code is adding several offset, I'll need to add more printfs there to check if
it is correct. I am consulting
https://www.usb.org/sites/default/files/audio10.pdf but I am not sure if this
covers UAC2.

Stefan

> 
> 
> thanks,
> 
> Takashi
> 
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -2358,8 +2358,10 @@ static int build_audio_procunit(struct mixer_build *state, int unitid,
>  	for (info = list; info && info->type; info++)
>  		if (info->type == type)
>  			break;
> -	if (!info || !info->type)
> +	if (!info || !info->type) {
> +		pr_info("XXX unit %d to default_info\n", unitid);
>  		info = &default_info;
> +	}
>  
>  	for (valinfo = info->values; valinfo->control; valinfo++) {
>  		__u8 *controls = uac_processing_unit_bmControls(desc, state->mixer->protocol);
> @@ -2375,8 +2377,11 @@ static int build_audio_procunit(struct mixer_build *state, int unitid,
>  		}
>  
>  		map = find_map(state->map, unitid, valinfo->control);
> +		if (map)
> +			pr_info("XXX map found for unit %d\n", unitid);
>  		if (check_ignored_ctl(map))
>  			continue;
> +
>  		cval = kzalloc(sizeof(*cval), GFP_KERNEL);
>  		if (!cval)
>  			return -ENOMEM;
> @@ -2444,19 +2449,26 @@ static int build_audio_procunit(struct mixer_build *state, int unitid,
>  		kctl->private_free = snd_usb_mixer_elem_free;
>  
>  		if (check_mapped_name(map, kctl->id.name, sizeof(kctl->id.name))) {
> +			pr_info("XXX name copied from map: '%s' for unit %d\n", kctl->id.name, unitid);
>  			/* nothing */ ;
>  		} else if (info->name) {
>  			strlcpy(kctl->id.name, info->name, sizeof(kctl->id.name));
> +			pr_info("XXX name copied from info: '%s' for unit %d\n", kctl->id.name, unitid);
>  		} else {
>  			nameid = uac_processing_unit_iProcessing(desc, state->mixer->protocol);
> +			pr_info("XXX nameid=%d, unit %d\n", nameid, unitid);
>  			len = 0;
> -			if (nameid)
> +			if (nameid) {
>  				len = snd_usb_copy_string_desc(state->chip,
>  							       nameid,
>  							       kctl->id.name,
>  							       sizeof(kctl->id.name));
> -			if (!len)
> +				pr_info("XXX copy string desc '%s'\n", kctl->id.name);
> +			}
> +			if (!len) {
>  				strlcpy(kctl->id.name, name, sizeof(kctl->id.name));
> +				pr_info("XXX copy default name '%s'\n", kctl->id.name);
> +			}
>  		}
>  		append_ctl_name(kctl, " ");
>  		append_ctl_name(kctl, valinfo->suffix);
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