[PATCH AUTOSEL 6.16] HID: elecom: add support for ELECOM M-DT2DRBK

[Sasha Levin <sashal@kernel.org>]

From: Martin Hilgendorf <martin.hilgendorf@posteo.de>

[ Upstream commit 832e5777143e799a97e8f9b96f002a90f06ba548 ]

The DT2DRBK trackball has 8 buttons, but the report descriptor only
specifies 5. This patch adds the device ID and performs a similar fixup as
for other ELECOM devices to enable the remaining 3 buttons.

Signed-off-by: Martin Hilgendorf <martin.hilgendorf@posteo.de>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

**Backport Status: YES**

This commit should be backported to stable kernel trees for the
following reasons:

## Hardware Enablement Bug Fix
The commit fixes a functional bug where the ELECOM M-DT2DRBK trackball
mouse has 8 physical buttons but only 5 are usable due to an incorrect
HID report descriptor. This is clearly stated in the commit message:
"The DT2DRBK trackball has 8 buttons, but the report descriptor only
specifies 5."

## Minimal and Contained Changes
The patch is extremely small and low-risk:
- Adds one device ID definition (`USB_DEVICE_ID_ELECOM_M_DT2DRBK
  0x018d`)
- Adds the device to three existing device tables
- Reuses existing fixup logic by adding `case
  USB_DEVICE_ID_ELECOM_M_DT2DRBK:` alongside the already-supported
  `USB_DEVICE_ID_ELECOM_M_HT1DRBK_011C` case

## Follows Established Pattern
The code changes show this device shares the exact same fixup parameters
as the M-HT1DRBK_011C device (lines 104-113 in hid-elecom.c):
```c
case USB_DEVICE_ID_ELECOM_M_DT2DRBK:
case USB_DEVICE_ID_ELECOM_M_HT1DRBK_011C:
    /* Report descriptor format:
     - 22: button bit count
     - 30: padding bit count
     - 24: button report size
     - 16: button usage maximum
     */
    mouse_button_fixup(hdev, rdesc, *rsize, 22, 30, 24, 16, 8);
```

## No Risk of Regression
- The changes only affect the specific device ID (0x018d)
- No modifications to core HID subsystem logic
- Uses well-tested `mouse_button_fixup()` function already in use for
  multiple other ELECOM devices
- Cannot affect other devices or subsystems

## User Impact
Without this patch, users of the ELECOM M-DT2DRBK trackball cannot use 3
of the 8 physical buttons, significantly limiting the device's
functionality on Linux. This is the type of hardware enablement fix that
stable kernels should include to maintain proper hardware support.

## Similar Patches Precedent
The git history shows similar ELECOM device support additions have been
routinely added (e.g., commit 29f316a1d7e0a for M-HT1DRBK_011C device),
indicating this is standard practice for the HID subsystem.

 drivers/hid/hid-elecom.c | 2 ++
 drivers/hid/hid-ids.h    | 1 +
 drivers/hid/hid-quirks.c | 1 +
 3 files changed, 4 insertions(+)

diff --git a/drivers/hid/hid-elecom.c b/drivers/hid/hid-elecom.c
index 0ad7d25d98647..69771fd350060 100644
--- a/drivers/hid/hid-elecom.c
+++ b/drivers/hid/hid-elecom.c
@@ -101,6 +101,7 @@ static const __u8 *elecom_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 		 */
 		mouse_button_fixup(hdev, rdesc, *rsize, 12, 30, 14, 20, 8);
 		break;
+	case USB_DEVICE_ID_ELECOM_M_DT2DRBK:
 	case USB_DEVICE_ID_ELECOM_M_HT1DRBK_011C:
 		/*
 		 * Report descriptor format:
@@ -123,6 +124,7 @@ static const struct hid_device_id elecom_devices[] = {
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT4DRBK) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT1URBK) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT1DRBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT2DRBK) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1URBK_010C) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1URBK_019B) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1DRBK_010D) },
diff --git a/drivers/hid/hid-ids.h b/drivers/hid/hid-ids.h
index a687fbbb77b00..0e2b9be3bd8b3 100644
--- a/drivers/hid/hid-ids.h
+++ b/drivers/hid/hid-ids.h
@@ -448,6 +448,7 @@
 #define USB_DEVICE_ID_ELECOM_M_XT4DRBK	0x00fd
 #define USB_DEVICE_ID_ELECOM_M_DT1URBK	0x00fe
 #define USB_DEVICE_ID_ELECOM_M_DT1DRBK	0x00ff
+#define USB_DEVICE_ID_ELECOM_M_DT2DRBK	0x018d
 #define USB_DEVICE_ID_ELECOM_M_HT1URBK_010C	0x010c
 #define USB_DEVICE_ID_ELECOM_M_HT1URBK_019B	0x019b
 #define USB_DEVICE_ID_ELECOM_M_HT1DRBK_010D	0x010d
diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c
index 90be93bdb0895..416160cfde77b 100644
--- a/drivers/hid/hid-quirks.c
+++ b/drivers/hid/hid-quirks.c
@@ -412,6 +412,7 @@ static const struct hid_device_id hid_have_special_driver[] = {
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT4DRBK) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT1URBK) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT1DRBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT2DRBK) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1URBK_010C) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1URBK_019B) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1DRBK_010D) },
-- 
2.50.1