[PATCH] ALSA: usb-audio: Add boot quirk for Behringer CM1A

["Sebastian Dalfuß" <sd@sedf.de>]

After a power cycle and reenumeration, the Behringer CM1A* leaves its
MIDI endpoint inoperative. USB enumeration and driver binding
complete successfully, but MIDI outputs remain pending.

A GET_DESCRIPTOR request for the device descriptor, issued after USB
configuration, makes the endpoint operational. Add a one time boot quirk
to perform that request before ALSA initializes the device.

*
ID 1397:1234 BEHRINGER International GmbH CM1A

Signed-off-by: Sebastian Dalfuß <sd@sedf.de>
---
 sound/usb/quirks.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 4936d66..f82d7a6 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -850,6 +850,27 @@ static int snd_usb_accessmusic_boot_quirk(struct usb_device *dev)
 	return 0;
 }
 
+/*
+ * A post configuration device descriptor read is needed to make the CM1A
+ * operational after reenumeration.
+ */
+static int snd_usb_cm1a_boot_quirk(struct usb_device *dev)
+{
+	struct usb_device_descriptor *desc __free(kfree) = kmalloc_obj(*desc);
+	int err;
+
+	if (!desc)
+		return -ENOMEM;
+
+	err = usb_get_descriptor(dev, USB_DT_DEVICE, 0, desc, sizeof(*desc));
+	if (err < 0) {
+		dev_err(&dev->dev, "failed to read device descriptor: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
 /*
  * Some sound cards from Native Instruments are in fact compliant to the USB
  * audio standard of version 2 and other approved USB standards, even though
@@ -1682,6 +1703,8 @@ int snd_usb_apply_boot_quirk_once(struct usb_device *dev,
 	switch (id) {
 	case USB_ID(0x07fd, 0x0008): /* MOTU M Series, 1st hardware version */
 		return snd_usb_motu_m_series_boot_quirk(dev);
+	case USB_ID(0x1397, 0x1234): /* Behringer CM1A */
+		return snd_usb_cm1a_boot_quirk(dev);
 	}
 
 	return 0;

base-commit: 4c4e4be4edd5dbf5f7f6a3ef4fc0c243f2d01b3c
-- 
2.53.0