ALSA: usb-audio: detect implicit feedback on Roland devices

All the Roland/Edirol/BOSS USB audio devices that need implicit feedback
show this unambiguously in their descriptors, so it might be a good idea
to let the driver detect this.

This should make playback work correctly (at least with Jack) with the
following devices:
- BOSS GT-100
- BOSS JS-8 Jam Station
- Edirol M-16DX
- Roland GAIA SH-01

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 776c58c7cba0d4cbe289e5d002d4626619b32307..15b151ed4899c6032704d361b9c641d2b53b849f 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -298,6 +298,35 @@ static int deactivate_endpoints(struct snd_usb_substream *subs)
        return 0;
 }
 
+static int search_roland_implicit_fb(struct usb_device *dev, int ifnum,
+                                    unsigned int altsetting,
+                                    struct usb_host_interface **alts,
+                                    unsigned int *ep)
+{
+       struct usb_interface *iface;
+       struct usb_interface_descriptor *altsd;
+       struct usb_endpoint_descriptor *epd;
+
+       iface = usb_ifnum_to_if(dev, ifnum);
+       if (!iface || iface->num_altsetting < altsetting + 1)
+               return -ENOENT;
+       *alts = &iface->altsetting[altsetting];
+       altsd = get_iface_desc(*alts);
+       if (altsd->bAlternateSetting != altsetting ||
+           altsd->bInterfaceClass != USB_CLASS_VENDOR_SPEC ||
+           (altsd->bInterfaceSubClass != 2 &&
+            altsd->bInterfaceProtocol != 2   ) ||
+           altsd->bNumEndpoints < 1)
+               return -ENOENT;
+       epd = get_endpoint(*alts, 0);
+       if (!usb_endpoint_is_isoc_in(epd) ||
+           (epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
+                                       USB_ENDPOINT_USAGE_IMPLICIT_FB)
+               return -ENOENT;
+       *ep = epd->bEndpointAddress;
+       return 0;
+}
+
 /*
  * find a matching format and set up the interface
  */
@@ -393,6 +422,18 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
                        goto add_sync_ep;
                }
        }
+       if (is_playback &&
+           attr == USB_ENDPOINT_SYNC_ASYNC &&
+           altsd->bInterfaceClass == USB_CLASS_VENDOR_SPEC &&
+           altsd->bInterfaceProtocol == 2 &&
+           altsd->bNumEndpoints == 1 &&
+           USB_ID_VENDOR(subs->stream->chip->usb_id) == 0x0582 /* Roland */ &&
+           search_roland_implicit_fb(dev, altsd->bInterfaceNumber + 1,
+                                     altsd->bAlternateSetting,
+                                     &alts, &ep) >= 0) {
+               implicit_fb = 1;
+               goto add_sync_ep;
+       }
 
        if (((is_playback && attr == USB_ENDPOINT_SYNC_ASYNC) ||
             (!is_playback && attr == USB_ENDPOINT_SYNC_ADAPTIVE)) &&