[PATCH 6.12 172/242] cdc-acm: new quirk for EPSON HMD

Greg Kroah-Hartman
2026-04-08T18:47:28Z

From: Oliver Neukum <oneukum@suse.com>

commit f97e96c303d689708f7f713d8f3afcc31f1237e9 upstream.

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 <oneukum@suse.com>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/20260317084139.1461008-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/class/cdc-acm.c | 9 +++++++++
drivers/usb/class/cdc-acm.h | 1 +
2 files changed, 10 insertions(+)

--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1225,6 +1225,12 @@ static int acm_probe(struct usb_interfac
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*/
@@ -1748,6 +1754,9 @@ static const struct usb_device_id acm_id
{ 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; andrey.arapov@gmail.com */
.driver_info = NO_UNION_NORMAL, /* has no union descriptor */
},
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -114,3 +114,4 @@ struct acm {
#define SEND_ZERO_PACKET BIT(6)
#define DISABLE_ECHO BIT(7)
#define MISSING_CAP_BRK BIT(8)
+#define NO_UNION_12 BIT(9)