Daniel Mack wrote:
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.
For UAC2 devices, when the descriptors say so. For UAC1 devices, never (because UAC1 does not have this mode). It looks as if all UAC1-like devices that need this are actually marked as vendor-specific, so we have quirks for them anyway.
I attached a patch below, only compile-tested. Please also check the USB ID again, as I'm not sure whether you sent the right lsusb dump (the device name looks suspicious).
The actual device name is correct; the "DFU" was taken by lsusb from the usb.ids file and is wrong. (I've submitted the correct name.)
static int snd_usb_audio_next_packet_size(struct snd_usb_substream *subs) {
frames = min(capture->frame_count, subs->maxframesize);capture->frame_count -= frames;
This assumes that both streams are running continuously, and you have to make sure to start them at the same time to prevent the frame_count from overflowing or underflowing. In my UA-101 driver, I ensure that the buffer fill level is the same for both streams by submitting each playback packet with the same frame count as the corresponding capture packet; but I'm not sure which algorithm is more robust in practice.
/* if this stream is in implicit feedback mode, start the* capture stream now as the playback stream relies on the* amount of data we see on the capture IN endpoint.*/if (subs->stream->implicit_feedback && !capture->running) {int ret;capture->ops.retire = retire_paused_capture_urb;
set_interface?
ret = start_urbs(capture, runtime);if (ret)return ret;}- return start_urbs(subs, runtime);
I think you have to wait for the first capture packet to be received before you can start submitting playback URBs.
Regards, Clemens