[ALSA] usb-audio: work around wrong wMaxPacketSize on ESI M4U

Add a workaround for the ESI M4U that claims to support 32-byte packets
but ignores the remaining bytes of packets bigger than four bytes.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

1 files changed, 5 insertions, 1 deletions

diff --git a/sound/usb/usbmidi.c b/sound/usb/usbmidi.c
index 911f4482b5e1..99295f9b7691 100644
--- a/sound/usb/usbmidi.c
+++ b/sound/usb/usbmidi.c
@@ -965,7 +965,11 @@ static int snd_usbmidi_out_endpoint_create(struct snd_usb_midi* umidi,
         }
         /* we never use interrupt output pipes */
         pipe = usb_sndbulkpipe(umidi->chip->dev, ep_info->out_ep);
-        ep->max_transfer = usb_maxpacket(umidi->chip->dev, pipe, 1);
+        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;
+        else
+                ep->max_transfer = usb_maxpacket(umidi->chip->dev, pipe, 1);
         buffer = usb_buffer_alloc(umidi->chip->dev, ep->max_transfer,
                                   GFP_KERNEL, &ep->urb->transfer_dma);
         if (!buffer) {