[PATCH 16/31] ALSA: usb-audio: scarlett2: Add Gen 3 mixer support

[Geoffrey D. Bennett]

On Tue, Jun 22, 2021 at 09:00:19AM +0200, Takashi Iwai wrote:
> On Mon, 21 Jun 2021 20:09:48 +0200,
> Geoffrey D. Bennett wrote:
> > 
> > Add mixer support for the Focusrite Scarlett 4i4, 8i6, 18i8, and 18i20
> > Gen 3 devices.
> > 
> > Signed-off-by: Geoffrey D. Bennett <g at b4.vu>
> > ---
> >  sound/usb/mixer.c               |   2 +-
> >  sound/usb/mixer_quirks.c        |   4 +
> >  sound/usb/mixer_scarlett_gen2.c | 260 +++++++++++++++++++++++++++++---
> >  3 files changed, 246 insertions(+), 20 deletions(-)
> > 
> > diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> > index 428d581f988f..ba4aa1eacb04 100644
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -50,7 +50,7 @@
> >  #include "mixer_quirks.h"
> >  #include "power.h"
> >  
> > -#define MAX_ID_ELEMS	256
> > +#define MAX_ID_ELEMS	512
> 
> This change requires the explanation.
> Usually the unit id is a byte per definition, so it can't be over
> 256.

Before making this change we were getting a buffer overflow in
mixer->id_elems[] (snd_usb_mixer_add_list()) because more than 256
controls were being added for the 18i20 Gen 3 device. I will send a
replacement patch with an updated comment.