From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Mack <daniel@caiaq.de>
Subject: Re: Need expert's advice - Fast Track Ultra (8R)
 dropping samples
Date: Tue, 12 Oct 2010 09:18:31 +0200
Message-ID: <20101012071831.GA7159@buzzloop.caiaq.de>
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To: Clemens Ladisch <clemens@ladisch.de>
Cc: tiwai@suse.de, alsa-devel@alsa-project.org, Felix Homann <linuxaudio@showlabor.de>
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On Fri, Oct 08, 2010 at 08:26:52AM +0200, Clemens Ladisch wrote:
> Felix Homann wrote:
> > @Daniel:
> > You asked for the output of lsusb. Are you thinking of modifying the
> > UA-101 driver yourself? Or something more generic?
> 
> I guess he wanted to look for UAC2 descriptors (which this device does
> not have).

Actually, I wanted to check whether the device marks the inbound
(capture) endpoint as isochronous with implicit data feedback usage.
Which it doesn't either.

> When (if) the driver has UAC2 implicit feedback support, it's easy to
> add a simple quirk that makes the FTU work.  (In that case, the UA-101
> driver can be merged back, too.)

I wonder if we can always fall back to implicit feedback in case a
playback substream does not have a syncpipe and does not have its
fill_max bit set.

Felix, can you add a

  printk(KERN_WARNING "%s() is_playback %d fill_max %d syncpipe %d\n",
  	 __func__, is_playback, subs->fill_max, subs->syncpipe);

at the end of set_format() in pcm.c and send us the output?

I have an untested patch ready which should add support for implicit
feedback, but I'm uncertain about the condition when to activate this
mode.


Daniel