cdc-acm: new quirk for EPSON HMD

This device has a union descriptor that is just garbage
and needs a custom descriptor.
In principle this could be done with a (conditionally
activated) heuristic. That would match more devices
without a need for defining a new quirk. However,
this always carries the risk that the heuristics
does the wrong thing and leads to more breakage.
Defining the quirk and telling it exactly what to do
is the safe and conservative approach.

Signed-off-by: Oliver Neukum <[e-mail]>
Cc: stable <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/class/cdc-acm.c

···
 		if (!data_interface || !control_interface)
 			return -ENODEV;
 		goto skip_normal_probe;
+	} else if (quirks == NO_UNION_12) {
+		data_interface = usb_ifnum_to_if(usb_dev, 2);
+		control_interface = usb_ifnum_to_if(usb_dev, 1);
+		if (!data_interface || !control_interface)
+			 return -ENODEV;
+		goto skip_normal_probe;
 	}
 
 	/* normal probing*/
···
 	},
 	{ USB_DEVICE(0x045b, 0x024D),	/* Renesas R-Car E3 USB Download mode */
 	.driver_info = DISABLE_ECHO,	/* Don't echo banner */
+	},
+	{ USB_DEVICE(0x04b8, 0x0d12),	/* EPSON HMD Com&Sens */
+	.driver_info = NO_UNION_12,	/* union descriptor is garbage */
 	},
 	{ USB_DEVICE(0x0e8d, 0x0003), /* FIREFLY, MediaTek Inc; [e-mail] */
 	.driver_info = NO_UNION_NORMAL, /* has no union descriptor */

drivers/usb/class/cdc-acm.h

···
 #define SEND_ZERO_PACKET		BIT(6)
 #define DISABLE_ECHO			BIT(7)
 #define MISSING_CAP_BRK			BIT(8)
+#define NO_UNION_12			BIT(9)