On Wed 07 November 2012 10:01:14 Daniel Mack wrote:
> On 07.11.2012 00:54, Jeffrey Barish wrote:
> > I guess that snd_usb_pcm_prepare is called by the core usb system to
> > prepare the snd driver. Anyway, snd_usb_pcm_prepare calls
> > configure_endpoint with a substream. Then configure_endpoint calls
> > snd_usb_endpoint_set_params with the data endpoint that corresponds to
> > the substream. snd_usb_endpoint_set_params calls data_ep_set_params with
> > the data ep and data_ep_set_params sets nurbs to 2 for the data endpoint.
> >
> > snd_usb_endpoint_set_params has code to call sync_ep_set_params when the
> > endpoint is type sync. sync_ep_set_params sets nurbs to 4 (why?).
> > However, snd_usb_endpoint_set_params never invokes the call to
> > sync_ep_set_params because ep->type is always data. Back up:
> > snd_usb_endpoint_set_params is called from configure_endpoint. It is
> > called from an if block contingent on the substream's having a sync
> > endpoint. It does. However, the call to snd_usb_endpoint_set_params
> > passes subs->data_endpoint as the first argument, so
> > snd_usb_endpoint_set_params simply repeats the operations it performed as
> > a result of the previous invocation. I presume that the first argument
> > to the second call to snd_usb_endpoint_set_params should be
> > subs->sync_endpoint.
> Eh. You clearly spotted a bug here. The rally interesting thing is that
> that it didn't bite us earlier, as it's in since 3.6.
Here's the diff. I can't figure out how to submit a patch.
--- sound/usb/pcm.c.orig 2012-11-08 11:43:57.309732860 -0700
+++ sound/usb/pcm.c 2012-11-08 11:41:06.512420658 -0700
@@ -456,7 +456,7 @@ static int configure_endpoint(struct snd
return ret;
if (subs->sync_endpoint)
- ret = snd_usb_endpoint_set_params(subs->data_endpoint,
+ ret = snd_usb_endpoint_set_params(subs->sync_endpoint,
subs->pcm_format,
subs->channels,
subs->period_bytes,
--
Jeffrey Barish
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