Re: Scarlett 16i16 4th Gen: I/O error on kernel 6.19-rc6 (works on 6.18)

["Geoffrey D. Bennett" <g@b4.vu>]

Hi Ruslan,

Audio playback for Focusrite USB interfaces is handled by the generic
USB audio driver (snd-usb-audio); the FCP driver I maintain only
handles the control protocol (mixer, routing, etc.) over a separate
USB endpoint — it's not involved in the actual audio data transfer.

I've CC'd the ALSA maintainers and linux-sound list to continue the
discussion there.

Regards,
Geoffrey.

On Sat, Jan 24, 2026 at 08:56:38PM +0500, Ruslan Garynin wrote:
>    Hi Geoffrey,
> 
>    I found a regression affecting Scarlett 16i16 4th Gen playback on kernel
>    6.19-rc6.
> 
>    Summary:
>    - Working: 6.18.6-zen1-1-zen
>    - Broken: 6.19.0-rc6-1-mainline
>    - Issue: I/O error on USB audio playback
>    - HDA/HDMI audio works fine on 6.19-rc6, so it's USB audio specific
> 
>    Test:
>      systemctl --user stop pipewire pipewire-pulse wireplumber
>      speaker-test -D hw:3 -c 18 -t sine -F S32_LE
> 
>    On 6.18 (works):
>      0 - Front Left
>      1 - Front Right
>      ...
>      15 - Channel 16
>      (sound plays)
> 
>    On 6.19-rc6 (fails):
>      0 - Front Left
>      Write error: -5,Input/output error
> 
>    Device info:
>      USB ID: 1235:821b
>      FCP driver loads OK: "Focusrite Control Protocol Driver ready"
>      Implicit Feedback Mode: Yes
>      No errors in dmesg
> 
>    /proc/asound/card3/stream0:
>      Format: S32_LE
>      Channels: 18
>      Endpoint: 0x01 (1 OUT) (ASYNC)
>      Rates: 44100, 48000
>      Sync Endpoint: 0x81 (1 IN)
>      Implicit Feedback Mode: Yes
> 
>    Note: This might get fixed on its own when mainline is updated further
>    before
>    the stable 6.19 release. I'm just reporting this in case it doesn't, so
>    you're
>    aware of a potential issue that could affect users when 6.19 changes
>    eventually
>    land in stable kernels.
> 
>    Let me know if you need any additional info or testing.
> 
>    Thanks for maintaining the Scarlett driver!
> 
>    Best regards,
>    Ruslan Garynin