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

[Stefan Sauer]

Another followup. I made a little python tool to dump all string descriptors via
pyusb - here is the code and the output for the device. No idea why lsusb hides
string descriptors.
https://gist.github.com/ensonic/00fa344a05c87093058a98a62893e3b4

I just dumped the first 100, since I haven't figured how to check for the number
of strings provided by the device. In any case there aren't any useful strings
beyond index=62, but the mixer.c code is accessing 82, 90. Will now figure how
it gets that number.

If there are ready made useful tools that I should use instead of writing them
myself in python, please let me know. Thanks

Stefan

Am 22.06.19 um 23:17 schrieb Stefan Sauer:
> Quick followup. Here is the lsusb -v output for the device:
> https://gist.github.com/ensonic/2d286a85bbf4aca25e6f36b3569849c3
> 
> I noticed two warnings:
> Warning: Junk at end of descriptor (17 bytes):
>         ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 00 00
> Could those be the cause? I don't now how to map the 'nameid' index to anything
> in the lsub output though.
> 
> Am 22.06.19 um 22:55 schrieb Stefan Sauer:
>> Hi,
>>
>> when I run
>> amixer -D hw:4 controls | sort -n -t = -k2
>>
>> I get the output below
>>
>> numid=1,iface=MIXER,name='KKKKKKKKKKKKKÃÃÃÃÃÃÃÃÃÃÃ Switch'
>> numid=2,iface=CARD,name='Internal Validity'
>> numid=3,iface=CARD,name='S/PDIF Validity'
>> numid=4,iface=CARD,name='ADAT Validity'
>> numid=5,iface=MIXER,name='Scarlett 18i20 USB-Sync Clock Source'
>> numid=6,iface=MIXER,name=' Switch'
>> numid=7,iface=CARD,name='Keep Interface'
>> numid=8,iface=MIXER,name='Master Playback Switch'
>> numid=9,iface=MIXER,name='Master Playback Volume'
>> numid=10,iface=MIXER,name='Master 1 (Monitor) Playback Switch'
>> numid=11,iface=MIXER,name='Master 1 (Monitor) Playback Volume'
>> ... lots of extra lines ...
>>
>> Please note the lines for numid=1 and numid=6. The first one contains some
>> garbage and the 2nd one look like it should start with another word.
>>
>> I now added some debug printing here:
>> https://github.com/torvalds/linux/blob/master/sound/usb/mixer_scarlett.c#L562
>>
>> and get output in dmesg:
>> [ 2971.642137] usb 1-2: Product: Scarlett 18i20 USB
>> [ 2971.642141] usb 1-2: Manufacturer: Focusrite
>> [ 2971.709773] new ctrl: name='Master Playback Switch', index=10, offset=1,
>> num=0: numid=8
>> [ 2971.709781] new ctrl: name='Master Playback Volume', index=10, offset=2,
>> num=0: numid=9
>> [ 2971.709788] new ctrl: name='Master 1 (Monitor) Playback Switch', index=10,
>> offset=1, num=1: numid=10
>>
>> 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
>>
>> I now added more debug prints into
>> https://github.com/torvalds/linux/blob/master/sound/usb/mixer.c#L2431
>> and its the code that calls snd_usb_copy_string_desc()
>> [ 5750.124123] usb 1-2: nameid=90, len=35
>> [ 5750.124157] usb 1-2: [51] PU [KKKKKKKKKKKKKÃÃÃÃÃÃÃÃÃÃÃ Switch] ch = 1, val = 0/1
>> [ 5750.125241] usb 1-2: nameid=82, len=1
>> [ 5750.125260] usb 1-2: [52] PU [ Switch] ch = 1, val = 0/1
>>
>> In both cases the returned len seems wrong and the function does not seems to
>> copy any useful string here. snd_usb_copy_string_desc() is just a wrapper around
>> usb_string().
>>
>> Is my hardware returning bogus data in usb descriptors? Can this be address
>> through some quirks table? Any other ideas?
>>
>> Thanks!
>> Stefan
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>>
> 
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