[alsa-devel] Resend: Incorrect sbits for snd-usb-audio

[Sander Jansen]

On Sun, Dec 8, 2013 at 3:20 AM, Takashi Iwai <tiwai at suse.de> wrote:

> At Fri, 6 Dec 2013 14:57:46 -0600,
> Sander Jansen wrote:
> >
> > Hi,
> >
> > I had send this out earlier back in September, but never got a response.
> >
> > I have a Focusrite Scarlett 2i4 USB Audio Interface. The audio format
> > exposed by ALSA for  this device is S32_LE. From the hardware specs and
> > lsusb. it supposed to only have a 24 bit resolution (with the LSB bits
> set
> > to 0):
> >
> > AudioStreaming Interface Descriptor:
> >         bLength                 6
> >         bDescriptorType        36
> >         bDescriptorSubtype      2 (FORMAT_TYPE)
> >         bFormatType             1 (FORMAT_TYPE_I)
> >         bSubslotSize            4
> >         bBitResolution         24
> >
> > When I query the sbits for this device, I expect it to return 24, but
> > instead it returns 32. Looking through the usb audio driver code, it
> > doesn't look like this information is actually exposed to userspace. The
> > 'parse_audio_format_i_type'  in usb/format.c merely returns the supported
> > formats, but doesn't include any msbits info. (and it doesn't look like
> it
> > can be easily changed to return the msbits info as well).
> >
> > Was this intentionally left out, or is this a missing feature in the
> driver?
>
> It's just because of laziness because almost no applications check the
> msbit but only the format type.  Feel free to send an enhancement
> patch.
>
>
>
Thanks for the clarification. I may give that a shot.

Sander