The patches below (extracted from kernel version 2.6.24.3) do bulk->int change and let the kernel recognize low-speed midi devices, the old 2.6.22.1-rt9 kernel said: "unknown device speed". If you're using a new kernel >=2.6.23 there is no need for this patch. But I use the older 2.6.22.1-rt9 kernel because it works much better with my laptop and jack, with newer ones I get xruns constantly. The patch consists of two parts: one for /usr/src/linux/drivers/usb/core/config.c: --- config.c 2007-07-10 20:56:30.000000000 +0200 +++ config.c.2.6.24.3 2008-01-24 23:58:37.000000000 +0100 @@ -124,6 +130,21 @@ endpoint->desc.bInterval = n; } + /* Some buggy low-speed devices have Bulk endpoints, which is + * explicitly forbidden by the USB spec. In an attempt to make + * them usable, we will try treating them as Interrupt endpoints. + */ + if (to_usb_device(ddev)->speed == USB_SPEED_LOW && + usb_endpoint_xfer_bulk(d)) { + dev_warn(ddev, "config %d interface %d altsetting %d " + "endpoint 0x%X is Bulk; changing to Interrupt\n", + cfgno, inum, asnum, d->bEndpointAddress); + endpoint->desc.bmAttributes = USB_ENDPOINT_XFER_INT; + endpoint->desc.bInterval = 1; + if (le16_to_cpu(endpoint->desc.wMaxPacketSize) > 8) + endpoint->desc.wMaxPacketSize = cpu_to_le16(8); + } + /* Skip over any Class Specific or Vendor Specific descriptors; * find the next endpoint or interface descriptor */ endpoint->extra = buffer; the second one for /usr/src/linux/sound/usb/usbaudio.c and .../usbmidi.c: Code: --- usbaudio.c 2007-07-10 20:56:30.000000000 +0200 +++ usbaudio.c.2.6.24.3 2008-01-24 23:58:37.000000000 +0100 @@ -3381,7 +3390,8 @@ *rchip = NULL; - if (snd_usb_get_speed(dev) != USB_SPEED_FULL && + if (snd_usb_get_speed(dev) != USB_SPEED_LOW && + snd_usb_get_speed(dev) != USB_SPEED_FULL && snd_usb_get_speed(dev) != USB_SPEED_HIGH) { snd_printk(KERN_ERR "unknown device speed %d\n", snd_usb_get_speed(dev)); return -ENXIO; @@ -3455,7 +3465,9 @@ usb_make_path(dev, card->longname + len, sizeof(card->longname) - len); strlcat(card->longname, - snd_usb_get_speed(dev) == USB_SPEED_FULL ? ", full speed" : ", high speed", + snd_usb_get_speed(dev) == USB_SPEED_LOW ? ", low speed" : + snd_usb_get_speed(dev) == USB_SPEED_FULL ? ", full speed" : + ", high speed", sizeof(card->longname)); snd_usb_audio_create_proc(chip); --- linux-2.6.22.1-rt9/sound/usb/usbmidi.c 2007-07-10 20:56:30.000000000 +0200 +++ linux-2.6.24.3-rt3/sound/usb/usbmidi.c 2008-01-24 23:58:37.000000000 +0100 @@ -963,8 +983,10 @@ snd_usbmidi_out_endpoint_delete(ep); return -ENOMEM; } - /* we never use interrupt output pipes */ - pipe = usb_sndbulkpipe(umidi->chip->dev, ep_info->out_ep); + if (ep_info->out_interval) + pipe = usb_sndintpipe(umidi->chip->dev, ep_info->out_ep); + else + pipe = usb_sndbulkpipe(umidi->chip->dev, ep_info->out_ep); if (umidi->chip->usb_id == USB_ID(0x0a92, 0x1020)) /* ESI M4U */ /* FIXME: we need more URBs to get reasonable bandwidth here: */ ep->max_transfer = 4; @@ -976,8 +998,14 @@ snd_usbmidi_out_endpoint_delete(ep); return -ENOMEM; } - usb_fill_bulk_urb(ep->urb, umidi->chip->dev, pipe, buffer, - ep->max_transfer, snd_usbmidi_out_urb_complete, ep); + if (ep_info->out_interval) + usb_fill_int_urb(ep->urb, umidi->chip->dev, pipe, buffer, + ep->max_transfer, snd_usbmidi_out_urb_complete, + ep, ep_info->out_interval); + else + usb_fill_bulk_urb(ep->urb, umidi->chip->dev, + pipe, buffer, ep->max_transfer, + snd_usbmidi_out_urb_complete, ep); ep->urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP; spin_lock_init(&ep->buffer_lock); @@ -1323,6 +1351,13 @@ endpoints[epidx].out_ep = ep->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK; if ((ep->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) == USB_ENDPOINT_XFER_INT) endpoints[epidx].out_interval = ep->bInterval; + else if (snd_usb_get_speed(umidi->chip->dev) == USB_SPEED_LOW) + /* + * Low speed bulk transfers don't exist, so + * force interrupt transfers for devices like + * ESI MIDI Mate that try to use them anyway. + */ + endpoints[epidx].out_interval = 1; endpoints[epidx].out_cables = (1 << ms_ep->bNumEmbMIDIJack) - 1; snd_printdd(KERN_INFO "EP %02X: %d jack(s)\n", ep->bEndpointAddress, ms_ep->bNumEmbMIDIJack); @@ -1336,6 +1371,8 @@ endpoints[epidx].in_ep = ep->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK; if ((ep->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) == USB_ENDPOINT_XFER_INT) endpoints[epidx].in_interval = ep->bInterval; + else if (snd_usb_get_speed(umidi->chip->dev) == USB_SPEED_LOW) + endpoints[epidx].in_interval = 1; endpoints[epidx].in_cables = (1 << ms_ep->bNumEmbMIDIJack) - 1; snd_printdd(KERN_INFO "EP %02X: %d jack(s)\n", ep->bEndpointAddress, ms_ep->bNumEmbMIDIJack);