On 18.03.2013 10:30, Takashi Iwai wrote: > At Mon, 18 Mar 2013 10:15:44 +0100, > Daniel Mack wrote: >> >> On 18.03.2013 10:07, Takashi Iwai wrote: >>> At Sun, 17 Mar 2013 20:07:23 +0800, >>> Daniel Mack wrote: >>>> >>>> Thanks to Andreas, I got my hands on a Playback Design MPD-3 and hacked >>>> up some small hanges necessary to make it fully work with snd-usb. >>>> >>>> The device reports 0x80000000 in the bmFormats field of two of three of >>>> its alternate settings, which wrongly made the driver believe it's a >>>> usual PCM endpoint (actually due to a fix-up fallback). However, bit 31 >>>> of this mask in fact denotes 'raw data'. >>>> >>>> The effect of this issue is that in addition to the first altsetting with >>>> a bit depth of 24, the driver exposed 8-bit and 16-bit native audio >>>> formats on the raw data endpoints, which do not work as expected. >>>> >>>> Also, those devices need a 50ms delay after switching the USB interface. >>> >>> Thanks, applied to for-next branch. >>> >>> The remaining question is which PCM format is suitable for the raw >>> data. SND_PCM_FORMAT_SPECIAL should be OK, it won't regress at least, >>> as no apps support this format. >> >> Yes, I thought about that for a while as well. In fact, the data format >> the device supports on these altsettings is "DSD", but that doesn't have >> a defined value in the UAC2 spec (and strictly speaking, DSD is not even >> PCM). >> >> So when a device is as unspecific as 'raw data', there's not much we can >> do about that except for exposing the same level of uncertainty down to >> the apps, right? > > Yes. We can add a new format SND_PCM_FORMAT_RAW, but it's not much > better than SND_PCM_FORMAT_SPECIAL after all :) Yes. If at all, we should add a SND_PCM_FORMAT_DSD, and a quirk for that device. But given that there is no application for DSD in userspace either, we probably don't need to care. Thanks, Daniel _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
