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

[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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