Support for Maltron L90 keyboard media keys

The USB report descriptor sent by the Maltron L90 keyboard is invalid,
causing the media key reports not to be accepted.

This patch adds a driver which uses a report fixup to replace the
descriptor.

Signed-off-by: William Whistler <[e-mail]>
Signed-off-by: Benjamin Tissoires <[e-mail]>

drivers/hid/Kconfig

···
 	Say Y here if you want support for the multi-touch features of the
 	Apple Wireless "Magic" Mouse and the Apple Wireless "Magic" Trackpad.
 
+config HID_MALTRON
+	tristate "Maltron L90 keyboard"
+	depends on HID
+	---help---
+	Adds support for the volume up, volume down, mute, and play/pause buttons
+	of the Maltron L90 keyboard.
+
 config HID_MAYFLASH
 	tristate "Mayflash game controller adapter force feedback"
 	depends on HID

drivers/hid/Makefile

···
 obj-$(CONFIG_HID_LOGITECH_DJ)	+= hid-logitech-dj.o
 obj-$(CONFIG_HID_LOGITECH_HIDPP)	+= hid-logitech-hidpp.o
 obj-$(CONFIG_HID_MAGICMOUSE)	+= hid-magicmouse.o
+obj-$(CONFIG_HID_MALTRON)	+= hid-maltron.o
 obj-$(CONFIG_HID_MAYFLASH)	+= hid-mf.o
 obj-$(CONFIG_HID_MICROSOFT)	+= hid-microsoft.o
 obj-$(CONFIG_HID_MONTEREY)	+= hid-monterey.o

drivers/hid/hid-ids.h

···
 
 #define USB_VENDOR_ID_ALCOR		0x058f
 #define USB_DEVICE_ID_ALCOR_USBRS232	0x9720
+#define USB_DEVICE_ID_ALCOR_MALTRON_KB 0x9410
 
 #define USB_VENDOR_ID_ALPS		0x0433
 #define USB_DEVICE_ID_IBM_GAMEPAD	0x1101

drivers/hid/hid-maltron.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * HID driver for Maltron L90
+ *
+ * Copyright (c) 1999 Andreas Gal
+ * Copyright (c) 2000-2005 Vojtech Pavlik <[e-mail]>
+ * Copyright (c) 2005 Michael Haboustak <[e-mail]> for Concept2, Inc
+ * Copyright (c) 2008 Jiri Slaby
+ * Copyright (c) 2012 David Dillow <[e-mail]>
+ * Copyright (c) 2006-2013 Jiri Kosina
+ * Copyright (c) 2013 Colin Leitner <[e-mail]>
+ * Copyright (c) 2014-2016 Frank Praznik <[e-mail]>
+ * Copyright (c) 2010 Richard Nauber <[e-mail]>
+ * Copyright (c) 2016 Yuxuan Shui <[e-mail]>
+ * Copyright (c) 2018 William Whistler <[e-mail]>
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+/* The original buggy USB descriptor */
+static u8 maltron_rdesc_o[] = {
+	0x05, 0x01,        /* Usage Page (Generic Desktop Ctrls) */
+	0x09, 0x80,        /* Usage (Sys Control)                */
+	0xA1, 0x01,        /* Collection (Application)           */
+	0x85, 0x02,        /*   Report ID (2)                    */
+	0x75, 0x01,        /*   Report Size (1)                  */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x15, 0x00,        /*   Logical Minimum (0)              */
+	0x25, 0x01,        /*   Logical Maximum (1)              */
+	0x09, 0x82,        /*   Usage (Sys Sleep)                */
+	0x81, 0x06,        /*   Input (Data,Var,Rel)             */
+	0x09, 0x82,        /*   Usage (Sys Sleep)                */
+	0x81, 0x06,        /*   Input (Data,Var,Rel)             */
+	0x09, 0x83,        /*   Usage (Sys Wake Up)              */
+	0x81, 0x06,        /*   Input (Data,Var,Rel)             */
+	0x75, 0x05,        /*   Report Size (5)                  */
+	0x81, 0x01,        /*   Input (Const,Array,Abs)          */
+	0xC0,              /* End Collection                     */
+	0x05, 0x0C,        /* Usage Page (Consumer)              */
+	0x09, 0x01,        /* Usage (Consumer Control)           */
+	0xA1, 0x01,        /* Collection (Application)           */
+	0x85, 0x03,        /*   Report ID (3)                    */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x75, 0x10,        /*   Report Size (16)                 */
+	0x19, 0x00,        /*   Usage Minimum (Unassigned)       */
+	0x2A, 0xFF, 0x7F,  /*   Usage Maximum (0x7FFF)           */
+	0x81, 0x00,        /*   Input (Data,Array,Abs)           */
+	0xC0,              /* End Collection                     */
+	0x06, 0x7F, 0xFF,  /* Usage Page (Vendor Defined 0xFF7F) */
+	0x09, 0x01,        /* Usage (0x01)                       */
+	0xA1, 0x01,        /* Collection (Application)           */
+	0x85, 0x04,        /*   Report ID (4)                    */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x75, 0x10,        /*   Report Size (16)                 */
+	0x19, 0x00,        /*   Usage Minimum (0x00)             */
+	0x2A, 0xFF, 0x7F,  /*   Usage Maximum (0x7FFF)           */
+	0x81, 0x00,        /*   Input (Data,Array,Abs)           */
+	0x75, 0x02,        /*   Report Size (2)                  */
+	0x25, 0x02,        /*   Logical Maximum (2)              */
+	0x09, 0x90,        /*   Usage (0x90)                     */
+	0xB1, 0x02,        /*   Feature (Data,Var,Abs)           */
+	0x75, 0x06,        /*   Report Size (6)                  */
+	0xB1, 0x01,        /*   Feature (Const,Array,Abs)        */
+	0x75, 0x01,        /*   Report Size (1)                  */
+	0x25, 0x01,        /*   Logical Maximum (1)              */
+	0x05, 0x08,        /*   Usage Page (LEDs)                */
+	0x09, 0x2A,        /*   Usage (On-Line)                  */
+	0x91, 0x02,        /*   Output (Data,Var,Abs)            */
+	0x09, 0x4B,        /*   Usage (Generic Indicator)        */
+	0x91, 0x02,        /*   Output (Data,Var,Abs)            */
+	0x75, 0x06,        /*   Report Size (6)                  */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x91, 0x01,        /*   Output (Const,Array,Abs)         */
+	0xC0               /* End Collection                     */
+};
+
+/* The patched descriptor, allowing media key events to be accepted as valid */
+static u8 maltron_rdesc[] = {
+	0x05, 0x01,        /* Usage Page (Generic Desktop Ctrls) */
+	0x09, 0x80,        /* Usage (Sys Control)                */
+	0xA1, 0x01,        /* Collection (Application)           */
+	0x85, 0x02,        /*   Report ID (2)                    */
+	0x75, 0x01,        /*   Report Size (1)                  */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x15, 0x00,        /*   Logical Minimum (0)              */
+	0x25, 0x01,        /*   Logical Maximum (1)              */
+	0x09, 0x82,        /*   Usage (Sys Sleep)                */
+	0x81, 0x06,        /*   Input (Data,Var,Rel)             */
+	0x09, 0x82,        /*   Usage (Sys Sleep)                */
+	0x81, 0x06,        /*   Input (Data,Var,Rel)             */
+	0x09, 0x83,        /*   Usage (Sys Wake Up)              */
+	0x81, 0x06,        /*   Input (Data,Var,Rel)             */
+	0x75, 0x05,        /*   Report Size (5)                  */
+	0x81, 0x01,        /*   Input (Const,Array,Abs)          */
+	0xC0,              /* End Collection                     */
+	0x05, 0x0C,        /* Usage Page (Consumer)              */
+	0x09, 0x01,        /* Usage (Consumer Control)           */
+	0xA1, 0x01,        /* Collection (Application)           */
+	0x85, 0x03,        /*   Report ID (3)                    */
+	0x15, 0x00,        /*   Logical Minimum (0)              - changed */
+	0x26, 0xFF, 0x7F,  /*   Logical Maximum (32767)          - changed */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x75, 0x10,        /*   Report Size (16)                 */
+	0x19, 0x00,        /*   Usage Minimum (Unassigned)       */
+	0x2A, 0xFF, 0x7F,  /*   Usage Maximum (0x7FFF)           */
+	0x81, 0x00,        /*   Input (Data,Array,Abs)           */
+	0xC0,              /* End Collection                     */
+	0x06, 0x7F, 0xFF,  /* Usage Page (Vendor Defined 0xFF7F) */
+	0x09, 0x01,        /* Usage (0x01)                       */
+	0xA1, 0x01,        /* Collection (Application)           */
+	0x85, 0x04,        /*   Report ID (4)                    */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x75, 0x10,        /*   Report Size (16)                 */
+	0x19, 0x00,        /*   Usage Minimum (0x00)             */
+	0x2A, 0xFF, 0x7F,  /*   Usage Maximum (0x7FFF)           */
+	0x81, 0x00,        /*   Input (Data,Array,Abs)           */
+	0x75, 0x02,        /*   Report Size (2)                  */
+	0x25, 0x02,        /*   Logical Maximum (2)              */
+	0x09, 0x90,        /*   Usage (0x90)                     */
+	0xB1, 0x02,        /*   Feature (Data,Var,Abs)           */
+	0x75, 0x06,        /*   Report Size (6)                  */
+	0xB1, 0x01,        /*   Feature (Const,Array,Abs)        */
+	0x75, 0x01,        /*   Report Size (1)                  */
+	0x25, 0x01,        /*   Logical Maximum (1)              */
+	0x05, 0x08,        /*   Usage Page (LEDs)                */
+	0x09, 0x2A,        /*   Usage (On-Line)                  */
+	0x91, 0x02,        /*   Output (Data,Var,Abs)            */
+	0x09, 0x4B,        /*   Usage (Generic Indicator)        */
+	0x91, 0x02,        /*   Output (Data,Var,Abs)            */
+	0x75, 0x06,        /*   Report Size (6)                  */
+	0x95, 0x01,        /*   Report Count (1)                 */
+	0x91, 0x01,        /*   Output (Const,Array,Abs)         */
+	0xC0               /* End Collection                     */
+};
+
+static __u8 *maltron_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+				  unsigned int *rsize)
+{
+	if (*rsize == sizeof(maltron_rdesc_o) &&
+	    !memcmp(maltron_rdesc_o, rdesc, sizeof(maltron_rdesc_o))) {
+		hid_info(hdev, "Replacing Maltron L90 keyboard report descriptor\n");
+		*rsize = sizeof(maltron_rdesc);
+		return maltron_rdesc;
+	}
+	return rdesc;
+}
+
+static const struct hid_device_id maltron_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ALCOR, USB_DEVICE_ID_ALCOR_MALTRON_KB)},
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, maltron_devices);
+
+static struct hid_driver maltron_driver = {
+	.name = "maltron",
+	.id_table = maltron_devices,
+	.report_fixup = maltron_report_fixup
+};
+module_hid_driver(maltron_driver);
+
+MODULE_LICENSE("GPL");