HID: redragon: Fix modifier keys for Redragon Asura Keyboard

This adds a new driver for the Redragon Asura keyboard. The Asura
keyboard contains an error in the HID descriptor which causes all
modifier keys to be mapped to left shift. Additionally, we suppress
the creation of a second, not working, keyboard device.
Signed-off-by: Robert Munteanu <rombert@apache.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/Kconfig

@@ -574,6 +574,13 @@ config HID_MAYFLASH
 	Say Y here if you have HJZ Mayflash PS3 game controller adapters
 	and want to enable force feedback support.
 
+config HID_REDRAGON
+	tristate "Redragon keyboards"
+	depends on HID
+	default !EXPERT
+	---help---
+    Support for Redragon keyboards that need fix-ups to work properly.
+
 config HID_MICROSOFT
 	tristate "Microsoft non-fully HID-compliant devices"
 	depends on HID

drivers/hid/Makefile

@@ -86,6 +86,7 @@ hid-picolcd-$(CONFIG_DEBUG_FS)		+= hid-picolcd_debugfs.o
 
 obj-$(CONFIG_HID_PLANTRONICS)	+= hid-plantronics.o
 obj-$(CONFIG_HID_PRIMAX)	+= hid-primax.o
+obj-$(CONFIG_HID_REDRAGON)	+= hid-redragon.o
 obj-$(CONFIG_HID_RETRODE)	+= hid-retrode.o
 obj-$(CONFIG_HID_ROCCAT)	+= hid-roccat.o hid-roccat-common.o \
 	hid-roccat-arvo.o hid-roccat-isku.o hid-roccat-kone.o \

drivers/hid/hid-ids.h

@@ -605,6 +605,7 @@
 #define USB_VENDOR_ID_JESS		0x0c45
 #define USB_DEVICE_ID_JESS_YUREX	0x1010
 #define USB_DEVICE_ID_ASUS_MD_5112	0x5112
+#define USB_DEVICE_ID_REDRAGON_ASURA	0x760b
 
 #define USB_VENDOR_ID_JESS2		0x0f30
 #define USB_DEVICE_ID_JESS2_COLOR_RUMBLE_PAD 0x0111

drivers/hid/hid-redragon.c

+/*
+ *  HID driver for Redragon keyboards
+ *
+ *  Copyright (c) 2017 Robert Munteanu
+ *  SPDX-License-Identifier: GPL-2.0+
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+
+/*
+ * The Redragon Asura keyboard sends an incorrect HID descriptor.
+ * At byte 100 it contains
+ *
+ *   0x81, 0x00
+ *
+ * which is Input (Data, Arr, Abs), but it should be
+ *
+ *   0x81, 0x02
+ *
+ * which is Input (Data, Var, Abs), which is consistent with the way
+ * key codes are generated.
+ */
+
+static __u8 *redragon_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+	unsigned int *rsize)
+{
+	if (*rsize >= 102 && rdesc[100] == 0x81 && rdesc[101] == 0x00) {
+		dev_info(&hdev->dev, "Fixing Redragon ASURA report descriptor.\n");
+		rdesc[101] = 0x02;
+	}
+
+	return rdesc;
+}
+
+static int redragon_probe(struct hid_device *dev,
+	const struct hid_device_id *id)
+{
+	int ret;
+
+	ret = hid_parse(dev);
+	if (ret) {
+		hid_err(dev, "parse failed\n");
+		return ret;
+	}
+
+	/* do not register unused input device */
+	if (dev->maxapplication == 1)
+		return 0;
+
+	ret = hid_hw_start(dev, HID_CONNECT_DEFAULT);
+	if (ret) {
+		hid_err(dev, "hw start failed\n");
+		return ret;
+	}
+
+	return 0;
+}
+static const struct hid_device_id redragon_devices[] = {
+	{HID_USB_DEVICE(USB_VENDOR_ID_JESS, USB_DEVICE_ID_REDRAGON_ASURA)},
+	{}
+};
+
+MODULE_DEVICE_TABLE(hid, redragon_devices);
+
+static struct hid_driver redragon_driver = {
+	.name = "redragon",
+	.id_table = redragon_devices,
+	.report_fixup = redragon_report_fixup,
+	.probe = redragon_probe
+};
+
+module_hid_driver(redragon_driver);
+
+MODULE_LICENSE("GPL");