[alsa-devel] A problem with USB audio devices and the UHCI scheduler

[Clemens Ladisch]

Monty Montgomery wrote:
> UHCI (and EHCI) use the endpoint's wMaxPacketSize for all bandwidth
> allocation.  My device supports all of its sample rates on the same
> altset, with a wMaxPacketSize matching the highest (96kHz) rate.  So,
> the HCD is reserving most of the USB bus's bandwidth regardless of the
> actual requirements.
>
> How should I approach fixing this in the driver?

You cannot fix it in the audio driver; bandwidth allocation is done in
the controller driver, and that one doesn't know that your device lies
about its bandwidth requirements.

> There's currently no means to communicate a desired bandwidth
> reservation to the HCD from USB audio, so I'd have to extend even the
> quirks.

The device is supposed to use alternate settings for this.

Can't you change its firmware?


Regards,
Clemens