At Tue, 17 Dec 2013 14:55:48 -0800, Sarah Sharp wrote: > > Hi Oliver and Takashi, > > I've noticed that in the last couple kernel releases or so, I can't get > USB webcams to suspend. It turns out that the USB sound interface is > keeping the device active, even when the device is not playing sound. > This goes back as far as 3.10, but I haven't tried older kernels. This > is testing on Ubuntu 13.10. > > Commit 88a8516a2128a6d078a106ead48092240e8a138f "ALSA: usbaudio: > implement USB autosuspend" went into kernel 2.6.39. The commit message > says the device is prevented from suspending if the pcm or midi channel > files are open. > > I plugged in a USB speaker, and ran lsof to see which files were open > (output is attached). AFAICT, only the USB sound device's control files > are open, and I don't have any midi files. > > Any ideas as to why USB sound auto-suspend isn't working? I don't know of any intentional changes regarding autosuspend in usb-audio since years. The central points are snd_usb_autosuspend() and snd_usb_autoresume() in sound/usb/card.c, so you can try to add some debug prints there for tracking more deeply what's going wrong. Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
