[PATCH 1/2] HID: elecom: rewrite report based on model specific parameters

[YOSHIOKA Takuma <lo48576@hard-wi.red>]

The report descriptor for EX-G wireless mouse (M-XGL20DLBK) is a bit
different from that for trackball mice such as DEFT. For such mouse, the
current `mouse_button_fixup` cannot be used as is, because it uses
hard-coded indices for a report descriptor.

Add parameters to `mouse_button_fixup` function, in order to support
fixing report descriptors for more models.

Signed-off-by: YOSHIOKA Takuma <lo48576@hard-wi.red>
---
 drivers/hid/hid-elecom.c | 41 ++++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/drivers/hid/hid-elecom.c b/drivers/hid/hid-elecom.c
index 8c712d4bc075..233188100884 100644
--- a/drivers/hid/hid-elecom.c
+++ b/drivers/hid/hid-elecom.c
@@ -11,6 +11,7 @@
  *  Copyright (c) 2017 Diego Elio Pettenò <flameeyes@flameeyes.eu>
  *  Copyright (c) 2017 Alex Manoussakis <amanou@gnu.org>
  *  Copyright (c) 2017 Tomasz Kramkowski <tk@the-tk.com>
+ *  Copyright (c) 2020 YOSHIOKA Takuma <lo48576@hard-wi.red>
  */
 
 /*
@@ -29,25 +30,26 @@
  * report descriptor but it does not appear that these enable software to
  * control what the extra buttons map to. The only simple and straightforward
  * solution seems to involve fixing up the report descriptor.
- *
- * Report descriptor format:
- * Positions 13, 15, 21 and 31 store the button bit count, button usage minimum,
- * button usage maximum and padding bit count respectively.
  */
 #define MOUSE_BUTTONS_MAX 8
 static void mouse_button_fixup(struct hid_device *hdev,
 			       __u8 *rdesc, unsigned int rsize,
+			       unsigned int button_bit_count,
+			       unsigned int padding_bit,
+			       unsigned int button_report_size,
+			       unsigned int button_usage_maximum,
 			       int nbuttons)
 {
-	if (rsize < 32 || rdesc[12] != 0x95 ||
-	    rdesc[14] != 0x75 || rdesc[15] != 0x01 ||
-	    rdesc[20] != 0x29 || rdesc[30] != 0x75)
+	if (rsize < 32 || rdesc[button_bit_count] != 0x95 ||
+	    rdesc[button_report_size] != 0x75 ||
+	    rdesc[button_report_size + 1] != 0x01 ||
+	    rdesc[button_usage_maximum] != 0x29 || rdesc[padding_bit] != 0x75)
 		return;
 	hid_info(hdev, "Fixing up Elecom mouse button count\n");
 	nbuttons = clamp(nbuttons, 0, MOUSE_BUTTONS_MAX);
-	rdesc[13] = nbuttons;
-	rdesc[21] = nbuttons;
-	rdesc[31] = MOUSE_BUTTONS_MAX - nbuttons;
+	rdesc[button_bit_count + 1] = nbuttons;
+	rdesc[button_usage_maximum + 1] = nbuttons;
+	rdesc[padding_bit + 1] = MOUSE_BUTTONS_MAX - nbuttons;
 }
 
 static __u8 *elecom_report_fixup(struct hid_device *hdev, __u8 *rdesc,
@@ -65,13 +67,28 @@ static __u8 *elecom_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 	case USB_DEVICE_ID_ELECOM_M_XT3URBK:
 	case USB_DEVICE_ID_ELECOM_M_XT3DRBK:
 	case USB_DEVICE_ID_ELECOM_M_XT4DRBK:
-		mouse_button_fixup(hdev, rdesc, *rsize, 6);
+		/*
+		 * Report descriptor format:
+		 * 12: button bit count
+		 * 30: padding bit count
+		 * 14: button report size
+		 * 20: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 12, 30, 14, 20, 6);
 		break;
 	case USB_DEVICE_ID_ELECOM_M_DT1URBK:
 	case USB_DEVICE_ID_ELECOM_M_DT1DRBK:
 	case USB_DEVICE_ID_ELECOM_M_HT1URBK:
 	case USB_DEVICE_ID_ELECOM_M_HT1DRBK:
-		mouse_button_fixup(hdev, rdesc, *rsize, 8);
+		/*mouse_button_fixup(hdev, rdesc, *rsize, 13, 15, 21, 31, 8);*/
+		/*
+		 * Report descriptor format:
+		 * 12: button bit count
+		 * 30: padding bit count
+		 * 14: button report size
+		 * 20: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 12, 30, 14, 20, 8);
 		break;
 	}
 	return rdesc;
-- 
2.29.2